Two tubes with felt-lined end caps.

As Mk1 but front tube is lined with sound-absorbing foam supported by stepped end caps

As Mk1 but front unit consists of a cross-drilled tube wrapped in J-cloth and supported by stepped washers.

Mk3 re-made with longer one-piece tube, more holes in cross-drilled tube and felt cloth instead of J-cloth.

The springs from a Soundbiter silencer each with with a nylon, felt-faced washer at the rear and a metal, felt-faced washer at the front.

Three tubes and three felt-lined discs.

Note that the back of the rear tube is open.