So another debate about machine pin sockets vs. standard (dual-wipe) sockets came up on one of the arcade repair-related groups I am a member of. And it, like just about every other older discussion about them, centered around not knowing our understanding what they are really supposed to be used for, and without fail, someone brings up the old “square peg in a round hole” argument.
So here are the details, people. All IC sockets are designed to protect the chip. For example, from damage due to soldering (excessive heat). But standard sockets are also good for facilitating replacement of a chip. It is relatively easy to remove and reinsert a chip when necessary.
But here is where machine pin sockets and standard sockets differ. Machine pin sockets are not designed to facilitate replacement. They are destined to retain. They are meant to grab onto a chip and Hold The Holy Shit out of it so that it can withstand a trip through a shake-n-bake (a colloquial term for an oven and/or vibration table used to test the robustness of assemblies) without loosing the chip.
With a standard socket, a good portion of the gripping power of its pins comes from the plastic carrier. If you have ever accidentally melted or damaged the plastic, you will notice a reduction in performance.
A machine pin socket does not get its strength from its plastic carrier, it gets it from the pins themselves, because of how they are constructed. So when you need a chip to stay in place, you use a machine pin socket. They may also not be good candidates for something that is often swapped out.
As for the round hole argument, the inside of a machine pin usually has square or triangular “grips” inside it to help improve contact with the IC’s pin. If you have the time, it might be worth carefully taking one apart to see how it works. It might just change your mind about them.