The kind of quick-release pin shown in the picture has a cap with an interior thread so it can be removed from the pin which has an exterior thread, revealing a center rod that extends axially down through the pin. My question is this: is the center rod a single piece that reaches down to the balls to cause them to protrude from the surface of the pin, or does that rod consist of two pieces, a long rod and a very short piece abutting it at the bottom that forces the balls outward when the center rod is pushed down into the pin?

The DIY connection, I want to make a cement mixer's barrel easy to remove from the motor shaft so I can power-wash the inside after using it. The motor isn't supposed to get wet but has no protection against water ingress. The unit ships with a large 12mm diameter pin and a cotter pin.

quick-release pin

P.S. If it weren't for the fact that the drum is rotating, and over the course of the 360 degree sweep there are some pieces of the motor mount that are in the way if the clip has twisted slightly, these clips would work fine. I mangled one when trying them out for this purpose.

hitch-pin clips

  • It's a well-formulated question, but who can say? That's a design/engineering thing that almost no one has personal insight into. I'd assume a single pin with a concentric spring, but....
    – isherwood
    Commented Jul 27, 2023 at 14:08
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    I don't understand how the internal construction of the center pin influences the need to remove the mixer bucket for cleaning. Perhaps you could clarify how the center pin construction is important? Commented Jul 27, 2023 at 14:18
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    A better question showing how the barrel is mounted, might get an answer if that type of pin will work. Those pins are just for holding, they do not provide any tension/tightest to the mounting.
    – crip659
    Commented Jul 27, 2023 at 14:48
  • @Triplefault: I was trying to learn if the pin I received in the mail was the way it was by design or as the result of damage enroute, possibly in sorting equipment at USPS. The manila envelope the pin was shipped in was quite mangled. The pin had a rod that consisted of two pieces, a long piece and a very short piece down near the balls. But I think the rod had been snapped where its diameter narrows. The spring pin was jammed and could not be depressed.
    – mr blint
    Commented Jul 27, 2023 at 15:38
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    @Crip659: unfortunately not for this mixer design. I've tried the kind of pin you're suggesting, but it twists in place and gets jammed. I'm confident that this quick release type of pin will work better than that, though it's not as simple as I'd like. I do take you point about the mess.
    – mr blint
    Commented Jul 27, 2023 at 16:27

1 Answer 1


The common way that these work is that the center shaft has an indentation that the balls can move into when the center pin is pressed. The center pin is a solid rod with an area that is a smaller diameter. When the pin is in the "locked" position, the balls sit against the large diameter of the pin. When the pin is pressed, the balls sit against the smaller diameter and can move inwards.

Believe it or not, I actually found a YouTube video of how these work, complete with a 3D printed cutaway. The balls are white on the right end, and the grey shaft sits between them you can see the indentation to the left of the balls.

Lock pin cutaway


Of course, every manufacturer is free to make things the way they want, but having a single piece rod is generally going to be less complicated and therefore less expensive than two pieces, so someone would need a good reason to deviate from this basic, proven design.

  • Thanks for a great answer. It is as I thought. The one I bought on a bidding site arrived with an immovable spring rod and when I was finally able to pull that rod out, a second smaller piece fell out. I think it must have suffered some mishap enroute, perhaps in the USPS sorting equipment. It was shipped from overseas in a small manila envelope with a bit of bubble-wrap.
    – mr blint
    Commented Jul 27, 2023 at 14:29
  • There's a lot of clever things in that design, not least being the combination of cross-drill and groove to seat the balls (albeit sacrificing a bit of strength). If the "handle" was threaded and secured with Locktite or similar it would be very difficult to work out the internal arrangement. Commented Jul 28, 2023 at 7:09

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