This mates with any pinion to drive through a right angle.
Original Meccano part produced from solid brass with one tapped cross hole for a grub screw (not supplied)
A used part with expected discolouration from age and use.
Original Meccano early 56T version of part 27a discontinued in the 1920's with a single tapped hole for a grub screw (not included)
A used part showing signs of discolouration through age & use