I need to replace the two crossmember set screws as they are missing. Believe they are M8 and can anyone advise what length these set screws should be.

There are no M8 set screws on a 2cv. (The only M8s anywhere are studs and nuts on the horn and the starter motor).
Do you mean the set screws that go into the brackets in each side of the body? (sometimes into captive nuts or sometimes into shaped brackets which support a parcel shelf/hammock).
If so these are M5x0.8 (or M5x0.75 on pre 1970 cars). From memory, I think the length of the threaded section is about 12mm: (long enough to thread in but not so long that it bottoms out).
https://www.ecas2cvparts.co.uk/screw-pl ... 4cf4e197b6

Yes thread lenght is 12.5mm, i think with 8 you mean the bolt head is for spanner 8?

Thanks Guys. Yes I meant the two set screws. In the book "How to restore a Citroen 2CV" by Lindsay Porter he quotes "8mm bolts", so I thought perhaps M8 meant 8mm. The 2CV is 1990 so will need then M5 x 0.8 to fit the captive nuts. Currently the boot lid is attached by zip cable on the n/s and nothing on the o/s, a bodge by the previous owner, a self appointed, so called "2CV Specialist" who had dismantled and reassembled 2CV, when resprayed in his ownership of several years of this car.

Perhaps there needs to be a new thread of 2CV Bodges of the Month on this forum.

Judging by the state of that cross member, it's the cross member you need to be replacing! Doesn't look like there's much left of it either end.

Has that been living by the coast or near a saltmine

I have a new crossmember just need to acquire the two set screws.

It's a good repair, the tywraps don't rust...

!

Have acquired both M5 set screws for the crossmember, but now need just the one M5 captive nut that the crossmember set screw requires. Does anyone either have a spare they don't need or know of a supplier of such a captive nut? Many thanks.