Gear box cover and floor board studs/screws

Mike the pest again !
I am in the process of screwing down the the gearbox cover and the floor boards in the car for the trimmer, can anybody advise on the size of the studs/ screws for the captive nuts in the chassis and around the bell housing opening for these items


I think they are all 5/16" BSF set screws, round head, slotted. I’ll check tomorrow and let you know if there is a difference.
You could pin them in place with conventional hex head s/screws every 2nd or 3rd spot to get the trimmer underway then replace them with a full set of the correct ones later. Tracking down an acceptable equivalent might take some time. Some holes are oversized to allow for fitting adjustment and these were covered with oval body washers.

I thought they were 1/4 BSF? Agree on slotted round heads.

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Yes, 1/4". I forgot that mine had all stripped due to corrosion. I need to make some square nuts to replace those in the cages.

Thanks Guys
I will try to source some now I know


Hi Mike,

Years ago I bought a few bags of nickel plated slotted round head 1/4” BSF setscrews from Spalding fasteners in the UK. Also for the MKV (and MKIV?) seat rails etc.

BTW it does pay off (IMHO) to make a small jig or tool for making the ends of the screws pointed, as many of (if not all) them originally were. I think it saves hundreds of curses and endless hours in trying to get the screws to engage in the threads of the captive nuts!

Also a tap and die in 1/4” BSF is a must. Those threads need to be clean and nice. Also I always put tar or something like Waxoyl in the threads to prevent seizing and rust! YMMV.



Thanks for the advise much appreciated