A collimation cap is a useful tool to help you carry out collimation of your telescope.
If you don’t have a collimation cap, you can quickly make one from the focuser blanking cap that came your scope.
Measure and mark the centre of the cap using the rear mouldings as a guide – then drill through with a small (1.5-7mm) drill bit. The smaller the hole, assuming you drill centre, the less potential misalignment of your eye.
Add foil to the rear of the cap to help with visibility of the cap during collimation.