Steering stem/top yoke size?

[Markracing10]

my bike is fitted with forks and yokes from a ducati 750ss but the top yoke/steering stem nut which is chrome plated steel has rusted up a bit so i went onto ebay and purchased a ducati yoke nut assuming it would fit, consiquently it does not so i went back onto ebay and purchased a rather sexy pro bolt trx yoke nut. This does not fit either as it is bigger than the steering stem threaded rod. The standard size for a trx yoke nut is supposed to be M22 but obviously my bike must have a steering stem from a different bike again (this is what happens when you buy a pre-modified bike) so can anyone confirm the actual size of the steering stem on a standard trx so i know i have not just been sent the wrong nut and even better if anyone knows of a steering stem which fits a trx which i may have on my bike??

[Mincehead]

Pro Bolt would confirm the stem diameter and thread pitch of a std TRX stem / top nut if you gave them a ring, they`re a good company but their products although being well made and finished are a tad expensive in all honesty.
As for your own stem, as fitted to your bike, check the stem overall thread diameter with a vernier guage or even two straight edges and a metric steel rule. An adjustable spanner can be utilised to do this or you might find you need an extra hand!
Then if you buy (or borrow) a thread guage, (they`re not expensive and will always be useful in the future), to ascertain the pitch of the metric fine thread you`ll know what you`re searching for and can contact Pro Bolt again to see if they would do an exchange.