Wheels Manufacturing Thin Flange Bottom Bracket Socket – Pro Kit. Thin Flange Bottom Bracket Socket Pro Kit These sockets are designed to create a tight grip on thin flange bottom brackets to avoid slipping while torquing cups into bike frames. These single-sided sockets are used for installing and removing 48.5mm 16-notch 52mm 16-notch and 50mm 12-notch bottom bracket cups.