Celestron 9.25 inch (23.5 cm) f/10 SCT versions with metric M3 screw threads (CPC 925, EdgeHD).
Note1: The CPC 925 SCT requires knobs with metric threads. The CPC 925 secondary can be identified by 1) a factory-installed plastic cover over the collimation screws; 2) black Phillips factory collimation screws; and 3) brand information on the inside of the housing, as shown in the above photo. The secondary housing cover will still fit when Bob's Knobs are installed, but can be left off if desired. The cover is cosmetic only and will not affect operation of the scope.
Note2: Celestron 9.25 inch SCTs manufactured prior to 2006 have standard 6-32 collimation screws and require knobs with standard threads. These telescopes can be identified by 1) no writing inside the secondary housing (except for the serial number); and 2) most have silver factory collimation screws. Do not use metric knobs on these telescopes.
Note3: A few 9.25 inch scopes have black Phillips factory collimation screws that have standard threads. It requires knobs with standard threads. Make sure the knob threads match the factory screw threads before installing the knobs.
Note4: These knobs sit inside the tall lip around the perimeter of the secondary, so they may be hard to grasp with two fingers. Adjustments can be made using a thumb or finger against the inside edge of the knob.