This device is an aperiodic (untuned) coupler that was designed to slip into the centre of a plug-in tuning coil to increase selectivity and cut out interference. There's no information with this device but it seems to act as a primary coil and uses inductive link coupling to boost the signal and couple it to the tuning coil that's acting as the secondary.

Dimensions are 74mm x 45 mm including metal fittings. Available from 1925 and cost 7 shillings and 6 pence.