Help! BB advice

[BarneyRubble]

I'm hoping the retrobike hive mind can help me. I recently bought a GT Bravado and some middleburn RS7 to go on it. BETD said I'd need a 118mm BB, so I managed to get a Shimano UN300 which slotted into the frame like a dream, but unfortunately is too short!
I can't find a 122.5mm Shimano one, so I bought an RPM one. I tried to fit it today but it just stops after a couple of turns. I don't want to push it because I think it will strip the threads. I've triple checked both BBs and they are definitely both English thread. I've refitted the shimano and sure enough it just glides in.

Can anybody help me work out what is going on? So frustrating!

 

[Stressed]

When you say 'too short' is it the shell or the axle?

 

[BarneyRubble]

When you say 'too short' is it the shell or the axle?

The axle. She'll is the correct 73mm wide.

 

[BarneyRubble]

The axle. She'll is the correct 73mm wide.

*shell

 

[Stressed]

Is the thread density on the RPM the same as the Shimano? If It's being awkward that may be the issue...

 

[BarneyRubble]

Is the thread density on the RPM the same as the Shimano? If It's being awkward that may be the issue...

How would I check? Can they be the same thread, but different density?

 

[Stressed]

24 TPI (threads per inch) is the English standard- should be a TPI rating on the RPM doc'...

 

[BarneyRubble]

 

[BarneyRubble]

Says 24 on the BB. Perhaps it is just badly made.

 

[CassidyAce]

I've got a nearly new 73mm, 122.5mm Shimano UN55 in the garage if you want it (£12 + postage). By 'nearly new' I mean that it was fitted and used for less than 100 miles, then removed.