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I

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okay we'll go into match drilling and

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fastener holes this is something that I

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touched on earlier which has to do with

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making sure that the holes match whether

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they're in their true position or not

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and by having a pilot hole in one part

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and then drilling all the way through

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with the mating pieces clamped in

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position this way you have a precision

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hole even if the holes are not in their

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troop positions because they can be off

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a little bit and still still be close

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enough and I have some examples of

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mismatched countersunk holes in the next

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figure now notice that this mismatch

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usually causes head bending which is bad

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news these these are cases in which see

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in the first one there the holes match

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the counter sunk is not in line so you

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have head bending where the era is up

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there the over here we even use the

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wrong counter snug hole and because

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there are two normal types 82 degree and

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100 degree countersunk heads and so if

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you use the wrong one you're in trouble

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here we have the holes parallel but not

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in line and here the holes weren't even

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parallel so we're real trouble there on

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bending on both of these so what you

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have here is a case in which you need on

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countersunk holes to use the same drill

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fixture put all the holes in through

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everything so that at least even if it's

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a little bit off the 90-degree alignment

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at least everything will match and

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you're in better shape that way than you

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are if you have one of them drilled

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right and the other one drilled it a

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now knife edges in a countersunk whole

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knife edges or stress risers and are to

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be avoided in fact the aerospace

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industry makes a big issue over this

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thou shalt not do it so if we go on to

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the next sheet it will show some

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examples of this and I can just talk

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from the examples there is a knife edge

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right here and you see that edge can be

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very jagged and developed cracks real

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easy so therefore you're not supposed to

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have that at all in a critical

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application you're supposed to make sure

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that you have enough thickness that you

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can counter sink and still have a piece

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left here to avoid that knife edge in

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fact having the countersink be no more

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than two-thirds of the thickness of the

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sheet is one of the criteria that the

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aircraft companies use then going to the

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next page now here we have dimpled and

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countersunk holes in this case we have

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the countersink in the bottom sheet we

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dimpled it just simply by hitting it

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with a tool to make this one fit so we

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could have a place surface up here and

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that's in in the case where you where

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the top sheet is too thin to countersink

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in it then we're both of them are too

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thin you can actually dimple both of

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them and still have a flesh surface now

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as I understand it this is still allowed

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mr. murky on small airplanes they still

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allow dimpling yeah Mario you put you

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fly so so this will this make you feel

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better they allow dimpled holes on small

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aircraft but they don't allow them on

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the big ones because the fact that where

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you deform the metal like that there's

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danger of developing cracks so so the

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the major aircraft manufacturers

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prohibit that now dowel pins there

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they're a very important thing and have

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an important function but sometimes

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people want to use them in way

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they shouldn't be used there are close

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tolerance pins which are used on lane

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mating components and that's really the

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their major function they usually

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mounted in what in one of the pieces

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with a slight interference fit then the

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meeting piece has a close tolerance hole

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the slip over it and you get good

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alignment of the pieces and then you

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bold them together or ever ever how you

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want to fasten together and you analyze

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the bolts for the total shear load and

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you don't use the dowel pins and bolts

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together to calculate the load because

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one of them is interference fit and the

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other one isn't so therefore the dowel

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pins would load up first so now if you

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want to put enough dowel pins in the

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carry all the load you could do that and

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then just hold them together with the

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intention with the bolts but you can't

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use two different fasteners that have

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different tolerances and say that both

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of them are going to carry load equally

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just like you don't use bolts and rivets

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together because the rivets would fail

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before the bolts pick up any load

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because the rivets and her parents fit

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the mold isn't so so that's that's the

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way that they're supposed to be used now

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you can design them to carry all the

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cheer load although normally you don't

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and now here's here's one of the things

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you can run into with dowel pins if you

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put them in blind holes they're kind of

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hard to remove so particularly if it's a

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solid pin so it's a lot better to have a

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through-hole to put a dowel pin in so

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you can take a punch to the back side

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and knock the thing out or use a vetted

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been with a groove or a flat edge for

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blind installations is to make sure you

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get the thing out and tapered dowel pins

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are available and pins with external

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serrations or ridges to prevent pin boat

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rotation so you drive the thing in place

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and it has the Russians on the edge of

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it that keeps it and rotating now sure

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allowables for dowel pins are usually

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determined by the

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manufacturers test program because a lot

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of the times the irregularity of the

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cross section means it is difficult for

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you to calculate the cross sectional

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area that you have so it's easier to use

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the manufacturers values for it so some

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of the common types of dowel pins that

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we have here is a plain solid one and

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pebble greened even this one is one of

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the ones that we Fred year since people

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made for me with some sort of a new

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system that they had gave it kind of a

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rough surface then we go to the drilled

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and tapped dowel pin with vents these

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are these even have little grooves

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around them so that they will vent and

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you can pull them out and then they have

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a drilled and tapped hole so that you

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can run a threaded rod in there of some

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kind or screw and actually pull the

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thing out with the ride here is a groove

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dowel pin and this one actually this

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this groove is on it to give it a little

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bit of compressibility you so this the

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grooved end would be slightly larger and

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that then you can pound it in and the

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groove will close up on some as you're

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pounding it in which is because you

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notice the groove doesn't go all the way

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down it is just it to one end then this

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is a vented dowel pin here and the

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groove does go all the way down so that

167
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you can get so she don't pull any vacuum

168
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when you put the thing in the blind hole

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now here's a tape that that I like and

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we use some of these because you can

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pull them this is the tapered dowel pin

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with a jacking net so that one you can

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slap it in the hole and then when you

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get ready to take it out all you got to

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do is tighten the nut up and that will

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pull it

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so those those are pretty pretty good if

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you if you've got a place where you can

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use them that way now roll pins are

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sometimes called spring pins are

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actually made by rolling a piece of thin

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alloy steel or stainless steel to a

183
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given diameter with a temper on each end

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of it so you can take a hammer and drive

185
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it in the hole it's then heat-treated a

186
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real high hardness and the coiled cross

187
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section on it decreases in diameter as

188
00:10:03,279 --> 00:09:59,599
you're driving it so that you have an

189
00:10:05,289 --> 00:10:03,289
interference fit now the slotted tubular

190
00:10:08,079 --> 00:10:05,299
pin is one that it's not really rolled

191
00:10:10,659 --> 00:10:08,089
up it's just a cylindrical piece of

192
00:10:14,739 --> 00:10:10,669
tubing with a slight cut in it and you

193
00:10:16,869 --> 00:10:14,749
can use that also SI spring pin so

194
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there's one of each shown on the next

195
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page here here is the roll pin which is

196
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wound up if you look at that one I

197
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believe you can see it better there that

198
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it's actually overlapped rolls of

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material so that it will develop more

200
00:10:36,909 --> 00:10:33,799
load of course than the single slotted

201
00:10:41,739 --> 00:10:36,919
tubular pin here these are used for

202
00:10:44,349 --> 00:10:41,749
installing cranks and I know that I've

203
00:10:48,369 --> 00:10:44,359
seen them used on bicycle cranks to hold

204
00:10:49,809 --> 00:10:48,379
them together and they're easy to tap in

205
00:10:51,969 --> 00:10:49,819
place and if they're in a through-hole

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then you can take a punch and knock them

207
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the once again the load carrying

208
00:11:04,329 --> 00:11:02,089
capabilities for these are usually

209
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determined and tabulated by the pin

210
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manufacturer because due to the

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00:11:14,820 --> 00:11:08,059
irregularity of the cross section it's

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and that will conclude roll pins in our