Freehand snatch block

My son is about to go camping, and wished for snatch blocks to hoist bear bags into trees more easily. I suggested that we had the stuff around the house to manufacture this ourselves, and make it much lighter (useful for camping) than the expensive high-load snatch blocks available for sale.

  • 1" polyethylene rod
  • ½" aluminum rod
  • ½" x ⅛" aluminum strap
  • 2 x M5*8 pan-head screws
  • 2 washers
  • loctite

Lathe: Used a 10mm round carbide insert as a form tool to make a pulley. Drilled it ½" through. Drilled and tapped ½" aluminum rod ¾" deep M5 (because I have appropriate M5 screws), parted it off ¾" long. This is a bushing.

Mill: Two pieces: Cut ⅝" and ½" holes at opposite ends of the aluminum strap, about 3" long. (The ½" hole about ½" from one end, and the ⅝" hole about ⅝" from the other end. ⅝" is just because it was a good match for some carabiners we have; choose hole size and corresponding placement to match.)

Vice: Bent the aluminum straps together near the ⅝" hole ends so that the ⅝" holes touch.

Put loctite in both ends of the aluminum rod.


  • M5 screw
  • Washer
  • Screwed into bushing rod
  • One strap over bushing
  • Pulley over bushing
  • Other strap over bushing
  • Other washer
  • Other M5 screw
  • Tightened solidly onto loctite

(On this first pass, the ½" holes are closer to the end than the hole diameter because we changed our mind about design partway through, and I could have rounded the edges on the straps. But for a quick and dirty low-load snatch block set, I was pleased.)


Second set went way better and faster. Figured out how to bend the strap better, so it’s more even, and left more meat around the bushing for strength. This time I remembered to chamfer all the hard edges on the pulley.

The slight outward bend at the loose end of the strap means that when it is loaded, the straps will tend to pull away from the pulley and thus avoid binding.

I didn’t think to polish the outside of the bushing, and if we ever make another we’ll probably do that.

More pictures, just because…


Got a report: The snatch blocks worked well. :tada:


I got a request that the open hole should be ½" like the bushing hole on the next revision. Also, the square corners offend my sensibilities, so rounding the corners…

I’m having some trouble getting fasteners to show up in the right place in my assembly because I’m still learning the Assembly4 workbench, but so far the model looks like this:

Also, a set of blocks to 3D print or machine to form the bends at the right lengths and to the correct angles, using a vice or press, and accounting for 2° springback in the aluminum bar:

It’s wide enough to do two bar segments simultaneously, so that they are a properly matched set. :relaxed: The different lengths on the bottom block are references to set the lengths of the two ends of the bars.


Figured out how to add the hardware correctly.

I’m not done making drawings, but I think the model is at the point that someone else could reasonably benefit from it, so here it is:


My son and I wondered about strength. The ends around the holes of the strap are clearly the weak points. I realized that a ½" hole in ¾" strap was a total of ¼" cross section across the face of the straps, and two ⅛" straps back to back is also ¼" cross section through the straps, so I should be able to divide tensile strength in PSI by 16 for a good strength estimate.

Aluminum 6063 is weaker than 6061 but more corrosion-resistant, so using its yield tensile strength of 31000 psi with a 1.5 safety factor gives almost 1300 lbs safe working load, if supported at both ends by a ½" shaft; almost 2200 ultimate tensile strength. Realistically, it will be used with a rope or a thinner carabiner at the open end, but this seems safe to hoist a couple of backpacks at least. Given the 4000 psi (250 lbs per 1/16 square inch) difference between tensile yield strength and ultimate tensile strength, and 12% elongation at break, I would expect substantial deformation before failure.

I previously thought about rigging up a many-stage block and tackle in the frame of my hydraulic press to test it to destruction with a digital hang scale, but that now seems unnecessary as well as potentially more exciting than I’m really looking for.

Do you see any holes in this logic?


I think you are good with you estimates :smile: In my backpacking experience we just used a bear bag to put all the food in and hoist just that up. Of course I’ve seen a bear go for a scented stick of deodorant before as well :man_shrugging:
It’s also all well and good until the bears figure out they just need to go for the rope end tied down lower, which I’ve also seen. :astonished: :bear:

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Yeah, in Pisgah where I occasionally go camping, hoisting a bear bag is no longer allowed; the bears have gotten educated. Only bear canisters allowed, which is why I have two.

I’ve also experienced a bear taking down a well-hung pack and eating the food out of it. That was interesting. And slightly inconvenient, because we were a day away from any civilization.

My son was camping where bears haven’t yet gotten that educated, so hoisting bags is fine. That was the point of the snatch blocks; to make it easiest to hoist the bags. And it worked well enough that other campers who were with him want some of their own. :tada:


A couple of other points to consider. First of all aluminum can be hardened. And there are various finishes that can be applied to it that may add a small amount of additional durability. The second is that you can add to your punch outs say an insert of brass or some blend of steel alloy.

Since I am reading your topic on mobile I don’t have a means of examining your 3D file and detail to see if you added sleeves to protect your bearing mounts.

While I’m not directly familiar with the product you are trying to create. My experience in similar things, of the automotive world. My opinion is that the bulk of the material should someone stretch under stress. But your sleeves and eyelets if reinforced correctly should not stretch at all they should be ultra durable they will eventually shatter but they will not stretch.

Another thing to consider when developing a product. And I mean no disrespect as I have no idea your level in developing hardware. When I develop any piece of hardware I consider not just what it is I am trying to make but also how it will be made what material it will be made from, and how that material will be manufactured. A lot of durability can be found in the actual manufacturing process itself.

I do not know that this would increase durability but if it were fabricated as one single piece I suspect it might be stronger. And nowadays you have a couple of options in that regard. You could say send your CAD files for the two pieces to be cut out from sheet metal and then formed and assembled. Or you could send a fusion file directly to a company like exama tree who could fabricate the entire piece on a metal 3D printer. Or alternatively the part could be made directly from cast. Unfortunately I do not have data to indicate which of those methods of manufacturing would be superior in terms of durability.


And a follow-up at it there was a bunch of stuff I literally did not see this morning when I started reading this post and as I’m now reading it for the second time I’m observing a whole bunch of new information such as some actual pictures of attempts at constructing this manually. So I have a much better idea what you’re trying to put together. And I suppose what I’m thinking is a vast over engineering of a far simpler device.

And if I’m not mistaken to understand you’re trying to put together a simple pulley that you can use to secure food and trash away from bears? Sadly I have literally seen videos of bears climbing the tree across the branch and then going to grab the bag of the things that we’re hoisted up in the air. Bears are unfortunately more resourceful than we give them credit for and sometimes things hoisted up into the trees isn’t quite far enough out of reach.

Yeah. Work-hardening aluminum making it weaker is one of my concerns regarding safe working load. But I think there’s enough margin to hoist a pack or three.

That would add complexity and potential for bimetallic corrosion. I’d just use wider straps (1 inch) if I wanted to make it stronger, rather than chance making it more likely to corrode.

The whole point here is for the sides to be separate; that’s what makes it a “snatch block” — you can rotate the arms separately, put it across a rope, rotate the arms into place, hook through the eye, and hoist, without having to feed the working end of a rope through a pulley block.

Smarter Every Day had an episode on pulleys that featured snatch blocks, showing how convenient they are.

Oh, I’m definitely not making a product here! Certainly not going to sell these. Zero desire to do a side business with this, just sharing the idea.

I just now found a commercial product that is similar:

It’s 58g to my ~40g, but is $17 for something that is advertised to safely hold almost 2.5 tons and is intended to be used to hold a person, not just a bag. Anyone buying a product would be well served to buy something designed by someone who knows what they are doing!

Honestly if my son had asked for a snatch block one day earlier, I probably would have just bought this rather than making a set.

Because this is meant to be carried backpacking, light weight is paramount.

Yes, that’s why I said:

I’ve been hanging in my hammock in the middle of the night, woken by a bear trying to figure out how to get into my bear canisters a safe distance away (thankfully unsuccessfully, unlike when one got a well-hung pack from a tree lo these many years ago, before bear canisters were even a thing as far as I know).

Bear education seems to vary from place to place. There are places in the northeast where fewer kinds of bear canisters are allowed, because the bears have taught each other how to get into some of the designs. In other places, bears haven’t figured that out yet, and hoisting seems to be effective, maybe because there is sufficiently plentiful food otherwise that it’s not worth their trouble.

As it happens, on the camping trip my son went on, the smelliest food was in three bear canisters even though they weren’t required where they were, and they hoisted other (hopefully less interesting) stuff into the trees. And they weren’t bothered.


This just came across my twitter feed and made me think our disscusion here. :grin:


I put shoulders on the bushings so that I can avoid the weight of washers on the ends. There is no real need for washers on this.

I also shortened the arms a bit to remove unnecessary material.

I added (amateurish, that’s me!) drawings too:

It’s all pushed to gitlab.

I don’t know why I keep working on this when I can buy better ones for $17 :roll_eyes: I guess I’m having fun!


Successful failure!

Inspired by the 3D printing press brakes experiments I did a few years ago, I wanted to try 3D printing bending blocks to form the bends in the arms of the snatch blocks.

I modified my bend forming block and anvil to have guide pins on either side, and to have steps in the anvil to set the lengths for the pieces to bend.

I 3D printed the bend forming parts out of PETG. Mostly solid layers, lots of perimeters, with a few 80% inflil layers deep in the inside to speed up printing a bit.

I tried bending a scrap of ⅛" 6061. This… isn’t anywhere close to a 150° angle, and the plastic deformed.

I guess I should try PLA, but really at this point I think that the right thing is to redesign them a bit and mill them from solid aluminum instead. I need to think about the right way to do that.

Two more pieces on my scrap PETG pile, one very slightly bent piece of 6061 scrap, and back to the FreeCAD drawing board!

These will be interesting to machine. I wonder whether I need some more tools for this? :smiley:


No longer freehand! Here’s the update.