4" wheels with a 5/8" hole are meant to be used on a 4" pneumatic or 4" electric grinder with a 3/8" or M10 arbor (threads). The centering flange is 5/8". 4.5" angle grinders are meant to use 4.5" wheels with a 7/8" hole. They can also use thread on 5/8-11 attachments. The threads (arbor) are 5/8-11 but the centering flange is 7/8". Thicker 4" wheels with a 5/8" hole may fit on a 4.5" grinder but may be slightly off center as shown in the video. A 4" cutoff wheel will not center at all."
This reddit comment: "Angle grinder disks are 'Universal' these days. 125mm = 5 inch, 115mm = 4 1/2 inch. 100mm/4 inch grinders use 16mm/5/8in center holes."