I have a Crown Graphic that's in pretty good condition overall. I'd like to get the top rangefinder working. I have some steel dowel pins that I think will work for spacers (2x3mm and 2x4mm), and ball bearings of a couple of sizes.

I'm not sure what to use, though. Does anyone know the diameter of the ball bearing?

Also, I lack a plunger and end cap. I should be able to turn a new plunger on the lathe, and I can probably easily make an end cap out of nylon or some other material. Does anyone know the large and small diameters of the plunger, or other measurements? I know the two possible overall lengths (1.040" or 1.140"), but that's the only number I have.

Thanks

Site search > balls and spacers < all the terms selected, speed graphic help selected = 29 results of which ths one has the dimension you are looking for:
https://graflex.org/helpboard/viewtopic.php?t=4952&highlight=balls+spacers
and this service manual section has the measurement for the lower plunger.
http://www.southbristolviews.com/pics/Graphic/manual-pdf/TRFService.pdf

Excellent! Thank you.