Device for adjusting the length of the mast or boom in a windsurf or the like

In a windsurf mast or boom having internal and external tubes that are axially telescopically slideable relative to one another, a device for locking the tubes in selected axial relationships to one another, comprising a continuous annular elastomeric ring having an inner diameter which is no greater than the outer diameter of said internal tube and having a circular cross-section at all radial planes thereof so that said ring can be easily and rapidly axially moved along said internal tube by rotating the same on said tube, the outer surface of the telescoping portion of said inner tube being essentially devoid of any circumferentially extending grooves thereon which can act as a seat for said elastomeric ring, a bushing member carried by said external tube for slidingly receiving said internal tube, said bushing member including a seat thereon to receive said elastomeric ring, and a squashing member cooperative with said bushing member, at least one of said members including an elongated conical surface thereon that makes an angle with the axis of said tubes in the range of from 10.degree. to 30.degree. and that has a maximum diameter greater than and a minimum diameter less than the outside diameter of said elastomeric ring, for squeezing said elastomeric ring between said conical surface and the outer surface of said internal tube thereby to axially lock said internal tube to said bushing member.