inglés al español Técnico/Ingeniería Ingeniería (general)

The text is about a pipe cutting machine. There's a Spare Part Catalogue with lists of spare parts, for example:

Item .....1
qty. .......1
Designation ........ Motor housing
*Subject* and Drawing ID-No .......... 3 7383 1011

I don't know how to translate 'subject' in this context, I've never seen this before, maybe it's very simple, but I'm a bit too tired to find it out... Thanks very much!