112mm does make sense. You would have bought this GSO Crayford,
http://agenaastro.com/gso-crayford-f...eed-112mm.html
A fine focuser. I use GSO focusers on all my scopes, 3 crayfords and one linear bearing with rigel systems electric stepper motor. Correctly adjusted they are perfect as far as I'm concerned.
Please post a pic when you get it installed.
Matt