Just had the LBS convert my wife's Schwinn Windwood cruiser

to a 3spd with a SA SRC3(II) hub built into the original wheel. I really thought I wanted a 22t cog instead of the 18t the hub came with. They built up the wheel and got it back to me in a day but, they didn't replace the 18t cog. The wrench said it would have to have a chain to accommodate the larger cog and we should try it with the 18t. It's ok but, I still want the 22t cog.

There is no way I could have built up the wheel. I think I can change the cog myself. I don't have a clue how to know what to look for in the way of a chain. Will it have some sort of master link? I have a chain tool if I need to push out/in a pin. Don't know how to size width or length of chain.

Suggestions?