25 to 37mm Stepping Ring
(25mm = some digital video cameras' filter thread size)
Can be used in conjunction with a 37mm to 52mm stepping ring to attach to Olivon DCA adaptor In conjunction with a T/52mm stepping ring, stepping rings can also be used to adapt SLR camera adaptors with only the T2 thread (eg Far-Sighted T77 Cam Adaptor, Visionary Cam Adaptor `A`) to the filter threads of most cameras.

(Note: Stepping ring pictured not this size)