I got a frame with another old Harley? Bike was sold as 1937 Harley, has girder front fork, any other manufacturers use girder fork, with single spring? Bolts all seem to be Metric, 24 mm axle nuts, 12 mm bolt heads, also foot pegs is single rod with U bolts over lower frame tubes, and rear break is on left side? Someone said It might be a early Triumph? Any pacific things to look for? On Harley? Or Triumph? appreciate any help, and feedback given. Cheers, Aaron.

  

Have you got any pics of the frame and fork to narrow down  your mystery? The description makes it very unlikely to be a 1937 Harley frame and Fork.

Girder front end were used by many different motorcycle manufacturers in the US but also throughout Europe until 1949,Harley did not use this type on any of their models,to set HD apart from the rest of the motorcycle manufacturing world the"Springer fork" was their"signature"so to say.

If the bolts are to be metric you can rule out the British bikes as the bolts and thread were Imperial sizes...

Are the axle bolts left hand threads? 

How are you measuring the nuts and bolts Aaron?  If the frame has been worked on in the last 80 odd years there would be a fair chance a 1/2" bolt could measure up as a 12 mm bolt.

Try to get a photo happenning.