The hope head doctor stem cap combats the problem of having to re tighten your headset two aluminium wedges pull together and expand inside any size of steerer giving you a solid thread to pull the stem down the hope head doctor combats the common problem of having to re tightening your headset two aluminium wedges simply pull together and expand inside any size of steerer giving you a solid thread to pull the stem down sound simple it is hope head doctor stem cap