126mm OLD is the standard for 5 to 7 speed. OLD increased to 130mm with the introduction of 8 speed.
Hubs for screw-on freewheels aren't speed/gear specific in the same way that freehubs for cassettes are (8 speed and above): the threaded part of the hub that the freewheel screws onto is the same.
Your current hubs will happily accept freewheels from 5 to 7 speeds.
Have a browse through Sheldon's glossary if any of the terms aren't familiar to you.
126mm OLD is the standard for 5 to 7 speed. OLD increased to 130mm with the introduction of 8 speed.
Hubs for screw-on freewheels aren't speed/gear specific in the same way that freehubs for cassettes are (8 speed and above): the threaded part of the hub that the freewheel screws onto is the same.
Your current hubs will happily accept freewheels from 5 to 7 speeds.
Have a browse through Sheldon's glossary if any of the terms aren't familiar to you.