Shock Mount Nut Size

My 1947 Mark IV front shock lower mount has a stud which goes through a hole in the axle. What size/thread is the bolt/nut? My nut went to Never-Never-Land, somewhere alongside the road. I measured the nut and determined it’s 5/8-inch. Definitely not SAE fine thread, so ordered 5/8-inch BSF. The nut screws loosely on the stud, but won’t tighten…just slips around. Any help will be appreciated.

Hello George, the parts catalog lists a part FN.109/L as 9/16" B.S.F. which is “Nut, securing Jaw in Axle Beam” for the front Armstrong shock absorbers. This same FN.109/L specification also is used in the front shock absorber at “Nut, securing Plate Assembly to Frame” for the C.2053 “Plate Assembly for Front Shock Absorbers”. You may compare one of the plate-securing nuts as needed to the missing nut application threads for verification.

Thanks Roger. I originally thought it might be 9/16, but couldn’t find one so convinced myself it must be 5/8.