Hi - the bolts/caps on the top of my DT400B (USA import) forks don't look original. Anybody know why the previous owner would have replaced the originals with these? Are they an 'upgrade'? Is there something missing? (Something that fits into threaded hole)? Any thought gratefully received. Anybody got a pair of standard bolts/caps for sale?

Look like Goki caps.  Popular aftermarket item in the day.  Missing the Schrader valve where you would add a few pounds of air/nitrogen.

Thanks for letting me know....

If you haven't done so already, check out CMSNL and Partzilla for which other models had those fork cap bolts and then include those in your fleabay search, as well as the part number. Also, they sometimes turn up in job lots and misecellaneous lots, but can take a bit of ferreting out.

Since they're gold, they might have been DG or another brand.  Might be something stamped in them.

Anyway, you need something like this for the air valves...  should be 1/8" NPT as that was a common size.