What is the hole diameter? I want it to replacea knob on my Celestron CG-5 mount.
It's approximately 0.25" in diameter, but not circular. It has the "flat side" to it which engages a similar flat face on the shaft it turns. I believe some have referred to this as fitting 6 mm shafts. (I'm using mine on a SkyWatcher EQ-5 telescope mount.)