.9mm hex that I use on my arcade machines. The handle is longer than I thought it would be (6.75 inches - only 171mm). The shaft is 3.25" (82mm) long, the grip itself is 3.5" (89mm) and about 5/8" (16mm) in diameter. . Very well built but like everything, what is so small it can break if you are not careful.I was hoping for a sturdier version but it works well.Reasonable cost - good grip and length.