Abstract: Apparatus and methods for releasably retaining any one of several tubular objects of different lengths between first and second retention members provide a rod insertable into any one of said tubular objects and a carriage slidable along that rod. The lengths of the rods are grouped into a plurality of different ranges of lengths. Stepped adjustment of the position of the carriage and second retention member to any of the ranges of lengths is provided for by means of a bayonet joint arrangement having as many distinct first bayonet joint portions as there are ranges of length, and having a second bayonet joint portion common to and interfitting with each of said first bayonet joint portions and being connected to the carriage. The first and second retention members are supported on the rod and on the carriage, respectively.

Abstract: The damping of transducers having a mass oscillating in the manner of a piston in a cylinder containing damping fluid on both sides of the cylinder is rendered adjustable by the provision of a conduit through the mass for the flow of damping fluid from and to either side of the oscillating mass. An adjustable valve is preferably provided in a part of that conduit for damping control through regulation of damping fluid flow.