1/4 turn system to quickly change the stock metal mounting heads for plastic heads (depending on wheel type). Comes with plastic mounting head, compatible with all mounting heads in the Bihr range. Includes: 1/4-turn male coupling for attachment to the changer arm 1/4-turn male coupling for attachment to the head that comes standard Plastic mounting head (standard size 10 to 23), with a second coupling 1/4 turn female