Stu,
Don't know that specific size and don't have one. Dovetails are usually M5, M6, or M8 on Asian or European made gear. American is UNC or whitworth 1/4, 5/16, 3/8" and U.K. can be either. Modern manufacturing is usually metric.
Being a 9.25" tube and Chinese made, it could be any of M5, M6 or M8.
If you don't get a definitive measurement from someone, I hope this narrows it down.
Joe
Hi I've had to source screws for my 79 C8 and my deforked CPC C9.25 and I ended up finding correct SS Philips head screws nuts and taps from United Fasteners in Adelaide (08) 83604622, on mine the metric and imperial was close but not close enough, its called 8 gauge so the tap size is UNC 8G x 32 or 8-32 it's an American thread, yours might be metric but check both as they are different threads per inch so stripping is a problem...they were real cheap and any specific fastener shop in your area should have them, Chrz...