Bob's Knobs for SkyWatcher & Celestron Newtonian Primary Fits: SkyWatcher Newtonian telescopes with factory collimation screws.Primary collimation Knobs: Black plastic, 16 mm (5/8”) diameter Threads: Stainless steel Primary Lock Knobs: Red plastic, 16 mm (5/8”) diameter Threads: Stainless steel Notes:Our knobs will fit only a primary with factory collimation screws. If your telescope already has factory collimation knobs (see Item B below) our knobs will not fit.The telescope optical tube assembly will clear the Dobsonian rocker box with primary knobs installed. Knobs with shorter screws and spacers replace the factory flathead Phillips collimation screws. Knobs with longer screws replace the factory set-style (grub) locking screws.Since the factory collimation and locking screws are close together, knobs must be staggered in height. The locking knobs protrude further than the collimation knobs, and they are red in color. Protect the locking knobs from damage, and do not support the OTA using the locking knobs as feet. Some SkyWatcher models are equipped with factory collimation and lock knobs. Our knobs will not fit these telescopes. Although the lock knob is small, its proximity to the collimation knob prevents replacing it with a larger knob. Furthermore, the primary adjustment knob is of a different design than our replacement knobs.
