The Velbon V4 is an aluminum boom arm with a geared extender. It attaches to the neck of a tripod replacing the existing head, which is then attached to the end of the arm. The arm has a grip knob at the rear end which is also the combined lock for the pan & tilt action. There's a locking wheel at the end to stop it slipping when in the upright position, and a friction knob to adjust the tension on the geared action. The base has a removable 1/4in thread spigot that can be exchanged with a 3/8in version, which is also supplied for use on older or larger pro spec tripods.
3/8 or 1/4in adaptors