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How to Build a Break Test Machine

This is a video about how our 3rd version of a break test machine works. Sometimes they are called tensile testers or slow pull machines but basically they pull a sample slowly until it snaps which is why we called ours SlackSnap. Carabiner tested here was a Hiatt England Steelie with a rumored MBS of 58kn donated by Luc Zavestoski. Soft releases pulled in these tests was standard tubular webbing with an MBS of 20kn. Here are links to the things we discuss in this video (a few are affiliate which help out this channel).

FRAMING I use 1/4" wall square tubing aluminum. Steel is better because it bends before it breaks compared to aluminum being quite the shit show if it snaps. I'm still alive but 1/8" wall steel tubing would be super good enough if not better. Hell, I've made my prototype out of 12 foot long 4x4 wood posts which you can easily get a 30kn break test machine. I don't think you need to overkill the ends. Just butt it up against the long sides and call it done. Triple wrap a spanset around the whole thing and call it bomber. Don't forget to put a cool name on the side!


We use a 3" bore x 1.5" rod x 60" in Slacksnap

We use a 5" bore x 2" rod x 24" in BoltBusters

3" bore x 1.5" rod x 48" long

3" bore x 1.5" rod x 60" long

4" bore x 1.5" rod x 48" long (biggest amazon offers)

5" bore x 2.25" rod x 24" long

(closest to boltbusters and a great price)

HYDRAULIC PUMP (DC Power) A 20 quart double acting pump - this is the one I bought (newest version they sell) and used and abused it the last 2 years -

A 15 quart double acting pump - should be plenty with the

3" hydraulic I have now. I got 20 quart for the bigger bolt buster hydraulic.

BATTERY The battery I have used for several years PLUS a charger included is at

CHARGER The battery charger I have (probably overkill for this)


Best prices on dyneema


LineScale3 is the best dynamometer to measure forces when doing normal activities NOT break test machines. Pre-order sale is still active as of Feb 2021 with a huge discount $699 instead of $795 at

Crane Scales - CHECK EBAY FIRST!!! That is where I get mine!!! Digital is the best.

Needle on a gauge is analog and keeps peak force without a limit of hz or speed of reading but a dial is not something I want in my tester. I want the number in digital form, otherwise you are guessing the exact force.

Dillion Juniors - variety of capacities (call for better prices)

S Beam

LabJack T7 Pro -

FLUID CONNECTORS - If you find an error or know this stuff better and have advice, please let me know at

Fittings are confusing!!! Learn about it at had the best prices and the stuff I needed.

***The CHIEF hydraulic cylinders I bought from Baileys have a SAE 8 or ORB 1/2" port (hole) so I have to reduce it to fit my quick connects. I use part number 6401-08-06 - 1/2" ORB Male x 3/8" NPTF Male hydraulic fittings found at

*** The Quick Connects I use are NPTF 3/8" because my hoses are NPTF 3/8" - part ISOA-SET-FP-06 - Set of 3/8" Hydraulic Quick Connects (Steel) x 3/8" NPTF Female

***The HOSES I have are 6 foot x 3/8" rated for 5,780psi - FA-R16-06-MP-MP-72 | Assembly: 3/8" R16 Hose with Male NPT x Male NPT, 72" long found at

***Pump - 95% sure it is a 1/4" NPTF fitting so I had to increase it to the 3/8" to fit my quick connects. I used 5404-06-04 - 3/8" NPTF Male x 1/4" NPTF Male hydraulic fittings found at

Our slacksnap and boltbuster date is on homepage

HMU at if you got lots of suggestions for drop tower

Please donate to help us with the drop tower at

Behind the Scenes


After Posting Thoughts


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Breaking Gear Fear

Edutainment has been a great way to help people understand their gear, and know the true limitations of it.  Watching HOW gear fails is more important than the force itself, as almost all gear is super good enough.  It's more important to share information on how to stay safe than it is to have a paywall.  We hope our stoke is contagious.

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