My brother-in-law has an Old Model 357 Blackhawk he'll let me use this summer as we travel - but it's missing the rear sight blade. I THINK the rest of the rear sight is there, but the blade with the notch in it is gone. I'm at the library, using their internet. Figured I'd ask here first as I start trying to see who might have one. Thanks for any help in locating one.

The Olde Models are the "without notch" type. I don't recall the correct terminology. Newer sights had a bump in the blade which fit to a notch in the base. Should be a bitty spring and adjustment screw besides.

one of these would be a direct fit for the gun? How much did they change the sight from Three Screw to Two Pin (Old Model to New Model)?

http://www.midwayusa.com/product/421942/ruger-rear-sight-base-assembly-complete-ruger-b...

I *think* that sight will work on an OM. I do know the Flattops used a Micro rear which had a round 'tang'.

The pivot pins are tiny. I modified a 1/16" punch with a hand drill and sandpaper so that it would clear. Don't know if my punch was oversized or if it's a necessary thing.

Haven't been to the Dungeon yet...I'll get back to you shortly.

https://www.gunpartscorp.com/Products/270730F.htm

costs 4.20$

they also have the screws and lots more:

https://www.gunpartscorp.com/Manufacturers/Ruger-33474/Revolvers-40405/OldModelBlackhaw...