It sounds like you have the older style of driveshaft nut which functions as 2 nuts being 1 piece with 2 threaded holes.

If this is true, the threads are British Standard and those are very hard to find bolts here in the US.

Can you believe it, British Standard? But a later Volvo parts book identifies the bolt as 'W5/16"-22 X 22' and that is British Standard.

New bolts are still available right from Volvo for $3.36 each. I don't have any new ones in stock, but I do have used ones.

FYI, there is supposed to be a lock plate that has bend over tabs to hold the heads of the bolts from turning after you tighten the bolts and bend the tabs, thus acting like a lock washer. Each lock tab has 2 holes and 2 bend over tabs so each lock tab holds 2 bolts.

The lock plates are are also still available from Volvo for $4.36 each and I do have those in stock, but you could use Loctite instead.

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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com