# Shear Pins

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#### cwbullet

##### Obsessed with Rocketry
Staff member
Global Mod
Guys,

What length of shear pins do you use? I am planning on ordering some and I found a source to order 1000 for what is costs for 100 elsewhere. What length do you use?

The source has #1, #2, #4, #5, and #6 screws.

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#### Steve Shannon

##### Well-Known Member
TRF Supporter
I think most of what I use are 1/4 inch or possibly 3/8 inch long. Anything longer than the thickness of both layers of body tube is just wasted.

#### Nytrunner

##### Pop lugs, not drugs
Echo what steve said

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
Guys,

What length of sheer pins do you use? I am planning on ordering some and I found a source to order 1000 for what is costs for 100 elsewhere. What length do you use?

The source has #1, #2, #4, #5, and #6 screws.
You’re gonna be more popular than a bale of dog barf at the next club launch!

#### Duster45

##### Well-Known Member
I use the ones that LOC sells. They are 3/8 inch long, and #1 and #4 diameters.

#### cwbullet

##### Obsessed with Rocketry
Staff member
Global Mod
I use #2 and #4. 1/4 to 3/8”. I am think about buying a couple thousand and selling them on our field by the hundreds.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
I use #2 and #4. 1/4 to 3/8”. I am think about buying a couple thousand and selling them on our field by the hundreds.
Sound retirement planning!

#### cwbullet

##### Obsessed with Rocketry
Staff member
Global Mod
Sound retirement planning!
You are right. But, I doubt there will be enough from rocketrysheerpins.com.

#### Jmhepworth

##### Well-Known Member
TRF Supporter
I get mine from McMaster Carr. Do you have a better source?

#### cwbullet

##### Obsessed with Rocketry
Staff member
Global Mod
I get mine from McMaster Carr. Do you have a better source?
Yes. I need to research them - what size, length?

#### Bat-mite

##### Rocketeer in MD
Do you screw yours in or friction fit? I screw mine in, and so I need enough hanging out after shear to grab with pliers and screw out. You may consider different sizes depending on thickness of tubing. 1/4" will do for most FG tubes. Too long can cause chutes to snag, so keep that in mind.

TRF Supporter

#### FredA

##### Well-Known Member
Get 2X your wall thickness - usually 1/4-inch - that way they don't protrude into rocket.

I use the same outside hole, but drill and tap a new inners on almost every flight.
Leave the old stubs in the hole - who cares.
All those holes only get seen once the rocket is apart and who cares???
I've had over 25 flights on the same rocket - a bit of swiss-cheese looking on the Ebay, but structurally sound.

And --- 100 shear pins / order ---> why that's only 20 flights ---> order 500!

#### augendoc

##### Member
Acetal or delrin is almost the same as nylon from a structural point of view. #2 imperial screws are about 2.18 mm in diameter so a M2 screw will be similar in size but weaker. A #3 imperial will be almost exactly the same as a M3 metric, though imperial #3 are pretty much impossible to find in nylon or acetal.

The Amazon acetal screws are slotted. I prefer philips as the entire edge of the head is smooth. Plus, the philips head will center any insertion or non-destructive removal tool like a small left hand drill bit (I like that idea) or a hardened screw removal tool.

i have both M2 and #2 nylon screws. The former purchased on eBay from Asia (pretty cheap and “free“ shipping) and the latter from McMaster-Carr, where the shipping is a killer unless you’re ordering 10,000 screws or combining with another order.

But look closely at the heads. The #2 imperial heads on my screws are slightly thinner but a little larger in diameter than the Asian M2 screws and the philips slot is very crisp and better molded. I found them easier to work with than the metric because of this aspect. McMaster also has metric nylon screws (even has M2.5) and I’ll bet they have crisp philips slots too. My Asian ones probably have JIS (Japanese Industrial Standard) slots, which are not quite the same fit as philips.

Way too much obsessive-compulsion on screw heads. Just go with McMaster-Carr and you wont be disappointed.

#### Rocketjunkie

But look closely at the heads. The #2 imperial heads on my screws are slightly thinner but a little larger in diameter than the Asian M2 screws and the philips slot is very crisp and better molded. I found them easier to work with than the metric because of this aspect. McMaster also has metric nylon screws (even has M2.5) and I’ll bet they have crisp philips slots too. My Asian ones probably have JIS (Japanese Industrial Standard) slots, which are not quite the same fit as philips.
The #2 are pan heads, the metric are regular round heads. I just push them in with my thumb. 5/64" drill for #2 and 7/64" drill for the #4. For 2 mm screws I would use a 1.8 or 1.9 mm drill. (Measure the screw thread OD and use the next smaller drill. When prepping the rocket next time, just poke out the ends. I always put an alignment mark on fiberglass rockets so I can use the same holes. I use shear pins on fiberglass airframes and friction fit with masking tape with cardboard body tubes.

#### KilroySmith

##### Well-Known Member

I bought some of these to try, but haven't yet:
no heads sticking out in the airflow...

I love Steve's idea of undersizing the hole and just pressing them in, though. I'll have to give that a try.

#### Steve Shannon

##### Well-Known Member
TRF Supporter
The only reason I screw them in is so I dont have to use a piece of tape over the head to make sure they dont fall out, its really the sam either way IMO.
I leave the hole oversized on the inside and just slightly undersized on the outer tube so the threads must upset slightly. They will not fall out. Then I easily pry the outer one out the next time I fly the rocket. The inner half just pushes out easily if it doesn’t fall out.

#### caveduck

##### semi old rocketeer
A quick check of my tube size database shows that 1/4" long pins give you 2x tube thickness for everything up through 4.5" glass and 4" blue tube, and 3/8" will handle everything else up through 11" Madcow fiberglass. So except for very special cases there's no need for anything over #4-40x3/8" or #2-56x1/4".

#### Jim Hinton

##### Well-Known Member
TRF Supporter
I thread the inner tube to receive the threads. Panel mount nuts are excellent for this. As a result, I use 4-40 X 1" nylon. There is enough 'tail'left after ejection to turn the remains out of the threads.

Jim