That is, you have two parts to mate and those thingies are supposed to help. You can find those in appliances, model kits, computer cases (to keep the bezel and the aluminum case proper together) and the like.
General example:
The projection fits into a hole, and then it's kept in place with a screw or bolt.
A VHS cassette:
Sometimes you have a flanged projection which doesn't require that, as it simply snaps in place sort of like this:
(Sorry about the poor draftsmanship, that crooked Christmas-tree-like monstrosity is supposed to be a flanged cylinder.)
What are they called? Dowels, projections, lugs don't seem correct. I'm writing a technical manual and I want to be extremely precise.
Best Answer
Boss In engineering, a boss is a protruding feature on a workpiece. A common use for a boss is to locate one object within a pocket or hole of another object.
See the pictures from this search for examples like yours.
Let me elaborate for you with this update:
Here is a fairly comprehensive book on plastic part design that covers bosses and other plastic part features in great detail. It’s a searchable book, and you might find it helpful for what you are doing.
Boss is the generic name given to the protruding feature in a mechanical design. As you recognize, the function of that protuberance varies, and it can be a protruding pin or a reinforced hole (or a protruding pin with its own hole (See here).
Terms like locating pin or tab and locating hole or slot are common. Pilot holes (in a boss) accept screws or threaded inserts. I haven’t seen any authoritative mention of terms like “male boss” and “female boss”. You can search the above-mentioned book yourself for terms that are used.
Bosses aren’t limited to plastic design, and any fabricated item might have a boss. The boss might be inserted into a second part in an assembly, fastened by whatever means the designer chooses (e.g. screwing, welding).