38-tooth gear to fit on the headstock spindle and engage with the headstock pulley as part of the backgear system.
The gear was made with two pressure angles:
1) 14.5-degrees for older lathes with a swing-type quadrant lever on the front face of the headstock, like this http://www.lathes.co.uk/boxford/img10.jpg
2) with a 20-degree angle for the Mk.2 lathes - the latter easily distinguished by the backgear engagement lever on the top face of the headstock like this: http://www.lathes.co.uk/boxford/img16.gif 
WHEN ORDERING PLEASE PUT IN ONE LINE OF YOUR ADDRESS EITHER 14.5 degrees or 20 degrees