Dropwire was introduced in early 1930's and used a small eccentric wheel known in the 'Vocabulary of Engineering Stores' as 'Clamps, Eccentric' for some reason
They can still be seen around if you look !
This is a twin wheel version
but most were a single wheel. See Herbert & Proctors 'Telephony' Volume 1 pages 1159/60
The cable was one pair with cadmium copper conductors known as 'Cable, I.R.V., Braided and Compounded' - (IRV = India Rubber Vulcanised)
Three types - Black, Grey or 'PBJ'.
Only the PBJ was still in use with a sliding copper clamp with a loop around an inch across which was dropped over a spindle when I started with the GPO as a YIT in the 1950's.