mrrabbit 

Common Hub Specs for Freewheel Type Hub

Dimension A = Freewheel Stop to End of Locknut
Dimension C = Outside Locknut to Outside Locknut


Regular Spacing

5-speed C = 120.00-122.00mm A = 29.00mm
6-speed C = 120.00-122.00mm A = 35.00mm (C = 125.00 - 127.00mm is optional)

Narrow Spacing - Road

6-speed C = 120.00-122.00mm OR 125.00-127.00mm A = 31.00mm
7-speed C = 125.00-127.00mm OR 130.00mm A = 36.00mm
8-speed C = 125.00-127.00mm OR 130.00mm A = 40.50mm (Not the best to go with...)

Narrow Spacing - MTB

7-speed C = 125.00-127.00mm (Not the best to go with...) OR 130.00-135.00mm A = 39.00mm
8-speed C = 130.00-135.00mm A = 40.50

Be aware that very old frames from the 50's and 60's often have dropout faces that are so large that the smallest outermost cog and chain will be contained within - i.e., spacing to 130mm for 8/9/10 has a high success rate for chain clearance near the seat stay.

Be aware that relatively newer frames from the 90s onward have stays that approach the OUTSIDE of the dropouts - i.e., they're offset to the outside. This creates room for 8/9/10 setups while providing chain clearance for the chain and seat stay while the chain is on the smallest cog.

Be aware however, that many entry to mid-range frames in the 80s had small dropouts combined with stays that hit the dropouts inline - not offset to the outside. Spreading to 130mm for 8/9/10 setups is not guaranteed to work - you need to test the clearance between the seat stay and the chain while the chain rests on the smallest outermost cog.

=8-)