Carton 100mm f/13 "MD" OTA Construction - GSO Focuser-to-Main Tube Adapter for Crayford
 

The focuser to main tube adapter with centering shim. (Click to see an enlarged image.)

 
To attach the GSO Crayford focuser to the main tube, I was very fortunate in that GSO also made focuser-to-main tube adapters for them. The astronomical supplies company Agena AstroProducts had one that was nearly perfect to allow me to connect the focuser to my main tube with limited rigging. To get a perfect fit, I shimmed the adapter with a .500" W x 10" L piece of stainless steel.