Mudguard bolts.

Its a good Question as most would have gone rusty and been replaced by now. They should be polished chrome 1/4 " cycle 26 tpi . I would fit flat with slightly rounded corners. . Chrome washers under the heads and the special domed washers between stays and guard. Most definately NOT metric. Who needs to carry multiple sets of spanners !, Satin chrome bolts with a show of light turning on the heads are also common on other parts .

... almost always denotes either SAE (Unified) threads or metric. I agree with Robert.

Andover Norton lists them

They list a set but I dont think they would be acceptable for a concours job. Otherwise ok for normal uaseage .

Pictures are hard to find. Can someone post a picture off guaranteed originals? The few in my collection of pics vary. But it looks as if they were flat, with normal chamfered edges and plain unmarked heads. And separate washers. Not like the domed head prewar ones. Cost saving, perhaps? The Andover Norton site picture doesn't show a top view. Metric bolts are marked with the grade of steel.

Polished chrome for mudguard Bolts .