1971 Roadster footrest bolts

5/16 UNC is what you want or 5/16 Whitworth has the same 18 threads per inch, just the thread form is 55 degrees as opposed to the unified form of 60 degrees. on a thread as small as that, the form will make little difference. (IMHO)

Unfortunately the answer is no unless somebody has changed a lot of them like they did on my 1971 Commando.

Below is whatyour cylinder head possibly should have. I am guessing that you have the breather coming off the camshaft side of the cases. Later engines with the breather at the back have more UNF threads

71Commando Twin Heads.

All threaded holesare Whitworth form (with 55 degree thread angle).

Commando 3 head/barrel studs - 3/8 BSF x 20tpi

Commando - intake rocker cover stud hole - 5/16 BSF x 22tpiCommando - 2 oil holes on side of head + 3 headsteady bolts -5/16 BSF x 22tpiCommando - intake port/manifold - 5/16 BSW x 18tpiCommando - rocker spindle cover plate screws (pre 66-short) - 1/4BSWx 20tpi

Commando - exhaust rocker cover studs- 1/4 BSW x 20tpi

Commando - Cylinder Head Bolts - 3/8 Cycle. Head Nuts - 5/16 Cycle

Crankcases

Thereare generally 3/8 Whitworth threads inside the cases and5/16 and 3/8Cycle nuts to go ontop of the studs. On later engines these nuts changed to 3/8 UNF x 24tpi.

Crankcases studsought to bea mix of 5/16 and 3/8 Cycle but my1971 enginecame withall beingUNF. Can someone else please confirm what should be correct here? UNF makes sense because nearly all the rest of frameuse these and UNC threads.

I will have to go with Phil's comments on this, but: His comments are specific to the engines. I believe that the frame bolts are all UNF.

Am I correct on this?

Mike

Yes generally the frame threads are UNF, also if you have a early bolt up rear brake drum and sprocket (pre cush drive) this will be UNF and the sleeve nuts are marked with a small turned groove. The earlier Dominator item is a cycle thread. ( generally cycle threads are all 26 tpi irrespective of dia but the thread form is 60 degrees)

This is relevent if you are fitting a set of Dominator sprockets to use a slimmer 520 O ring chain.

So you need a set of imperial AF spanners and sockets for the frame. A set of Whitworth spanners and sockets for the engine ( BSF/BSW/ Cycle) and a set of metric for your car unless it's an old Brit clunker!!