When did the J frame mainspring swivel change from being made of metal to polymer? What is the advantage to having this one plastic part inside my otherwise all metal 637 revolver? Does it function better or is it just less expensive to manufacture?

Not sure when, but I wish someone would offer metal replacements/upgrades. Seems wrong to have that 1 plastic part in the gun. My 1997 vintage 637-1 I bought new has it, so it must be prior to that.

I don't know the answer but would guess when they went from forged parts to MIM..
That's when I first saw them..
I only have one extra of the metal ones in my parts stash.

I have a 442 made in 1996 with a metal one.

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NRA Benefactor

I've never had any problems with the plastic ones but I would like the option of buying metal.

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Centennial Every Day