I've got a 336 RC .35 Rem made in 1957 (I think). It is a bit of an ugly duckling but I'm slowly working it back into shape. None of the available hammer extensions will fit. I don't really like them but I have a very low mounted scope and am a bit nervous the thumb will slip off the hammer. I may make a clamp on extension as a last resort but as I said, they are not my cup of tea. I'm curios if anyone knows if a later model hammer would fit this action? If so I wouldn't be afraid to modify the spare hammer to my liking. I'm thinking of TIG-ing on some additional material rather than a clamp on piece.

All the later hammers from Marlin that are undercut for hammer spurs are wider and will not fit your gun. There used to be companies that made spurs specifically for those old Marlins with the narrow hammers and no undercuts but I think that's mostly an Ebay item now. I personally don't like hammer spurs as they slow down lock time and have even been known to cause weak primer strikes. I don't slam my scopes down low on Marlins so I'm not forced to use a spur. If yours is a 1957 the serial number will begin with the letter P.

I've got two hammer spurs that either came on Marlins and came loose (because they were never right) or were bought for a Marlin .219 Zipper and didn't fit. I don't know where to find one that fits that era Marlin. Seems to be a common problem.

Thanks. By wider, I take it you mean the body of the hammer down at the pivot and trigger notch area and it won't fit into the action? A wider hammer spur shouldn't matter because that never goes into the receiver. I guess I should have measured my hammer before asking the question.

I don't remember my rifle having a letter in the serial number, but will pull it back out and look.

FWIW, Uncle Mike's lists 2 different hammer extensions for the Marlin 336;

#24520 for rifles built between 1957 and 1982.

#24580 for rifles built since 1983.

Yes, the body of the hammer is wider after a certain year. Somewhere in the 1960's.

I ran into the same situation with a P code.
I have a P code 336RC, which is a 1957, however there is a R code, listed as 1957-1958. Now getting to spurs, obviously Uncle Mikes has the Pre 83, which covers 82 back to 57. Now comes the hitch!!!, my P code 57 model doesn't seem to fit this category of hammer spurs., So I guess there's an early 57, and a later 57 model year, for certain things, hammers being one. Pic below shows my P code hammer, in the back, compared to a 68 AD model, which obviously uses the Pre 83 spur. I believe there is an old Williams #36, no longer offered, so its an Ebay, Gun Shows, etc. deal. So for the time being I used the 68 AD hammer. I thought I read awhile ago about hammer width differences, but it didn't seem to matter in this instance.
A few pics.

P code over AD code.


P code left.


P code in rear. Can easily see the undercut on the later hammer in front, also the evenness, as the older style is tapered.


Here's the 68 AD code hammer, with appropriate spur, in my 57 P code gun.

I was incorrect in thinking it was a 1957 rifle. The serial number starts with "M" which makes it a 1955 manufactured rifle. Some good info here. I'll keep my eye out for the correct hammer to modify, otherwise I'll look at making a short extension. The scope isn't so low you can't get to the hammer, but it would be near impossible with gloves on and the serrations aren't real sharp so the chances of it slipping are increased with the limited access. Thanks.

Jeff, thanks for the heads up. I just ordered two for the earlier Marlins.

You should try Outback Gun Parts for Marlin items. www.outbackgunparts.com