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:

What are these called?

The projection fits into a hole, and then it's kept in place with a screw or bolt.

Computer case.

A VHS cassette:

enter image description here enter image description here

Sometimes you have a flanged projection which doesn't require that, as it simply snaps in place sort of like this:

enter image description here

(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.

  • I’m not much of a DIY man, but your drawings look most like Rawlplugs to me (though I don’t think that’s what you’re after here) ..? – Janus Bahs Jacquet Jul 16 '13 at 16:24
  • @JanusBahsJacquet Do you mean a wall plug/expansion anchor? Not exactly, although the basics are the same. I'm not talking about a general purpose, separate fastener, it's more like a mortise/tenon configuration. The 'tenon' would be the projection embedded into Part 1 (say, a computer case bezel), the 'mortise' would be whatever hole it fits in. – Reddast Jul 16 '13 at 16:37
  • @Reddast as you noted, it does look similar to wall anchors- could it be something related to the winged plastic or toggle bolt anchors here? It also reminds me a little of a screw cast... – batpigandme Jul 16 '13 at 16:47
  • @batpigandme Related, yes, probably... but it doesn't really apply. I edited my question and added some pictures to further clarify what I mean. – Reddast Jul 16 '13 at 18:31

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).

  • Apparently we have a winner! That's exactly what I was looking for. I'll just add a parenthetical description in case the reader isn't familiar with the term. (Like the writer. :)) – Reddast Jul 16 '13 at 19:52
  • @Reddast, if you read Jim's linked material more carefully, you'll see that a "boss" is a protrusion with a hole where another object sits. That is not the object you described. Your protrusion (you know what I mean) does not house another object inside it, it goes into something else, like a hole, as in the jewel case hinge example. – Kristina Lopez Jul 16 '13 at 21:26
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    @KristinaLopez I had the same doubt, but then I landed on the Wikipedia page on the gender of connectors, which explains, using LEGO blocks as an example, that "[they] have "female" indentations on the lower surface, and "male" bosses or protrusions on the upper surfaces." TheFreeDictionary defines 'boss' (in a general/technical context) as a 'knob or knob-like protuberance' or a 'similar projection'. I think (perhaps wrongly?) that I can use "male boss" and "female boss". – Reddast Jul 16 '13 at 21:48
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    Well, Kristina, as an engineer of over 30 years experience, and who comes across these in my own designs quite often, I have to disagree. All of the example pictures (except the sketch with the Christmas tree clips) illustrate the boss. Even the hole into which a pin is located is most likely designed with what is generically called a boss for added strength (although a simple hole might be used in some cases). I assume the Christmas tree clips shown in his sketch were used to illustrate something that might snap into a boss. But the Christmas tree clips themselves are not examples of bosses. – Canis Lupus Jul 16 '13 at 21:52
  • @Jim, just to clarify, and with all due respect to your background, while some of the OP's examples, such as the first image which is tooled for a screw to be inserted, may be bosses, the pin in the jewel case and the barbed protrusion, 2 other of the OP's examples, are not bosses. Either way, I'm happy to say that I've learned something today - as usual on this site! :-) – Kristina Lopez Jul 16 '13 at 22:02

"Pin" is the term used for the jewel case hinged apparatus, per the details in the jewel case's patent:

. . . "The standard CD Case as a whole is asymmetrically formed around the optical disk which it holds, so that the holes and the pins forming the hinge are formed in such a case beyond the area required to contain such optical disk."


In an automotive context, your “flanged cylinders” are referred to as panel clips or trim clips. However, those are somewhat generic terms, and take in several varieties of clips. More-specific terms include panel clips, dart type; door trim panel clips; headlining trim clips. (Images 1, 2)

 panel clips, dart type jaguar headlining trim clips

For the projecting pegs, I have heard or seen them called stanchions (“vertical pole, post, or support”) most commonly, and sometimes posts, pegs, or (as Reddast mentioned) tenons.

  • Peg might be a good candidate, but it still sounds a bit too generic. I'm not sure about stanchion, as it seems to refer to a rather big vertical post not necessarily used to join two parts together. Tenon seems to apply exclusively to woodworking. I updated my question with new pictures. – Reddast Jul 16 '13 at 18:07

I'd probably call them barbed plugs. That search shows at least some others do too, so it would be a reasonable way to start looking if you wanted to buy some.

barb - a subsidiary point facing in the opposite direction to the main point ... intended to make extraction difficult.

You might also get somewhere if you searched for press-in plugs (or fasteners).

Some of the things in OP's pictures don't seem to have any special features designed to prevent the fastening from easily coming undone. Any such "passive" fixing is really just a type of locating lug.

  • I'm not talking about plugs you can buy and then use to join two parts together, in which case the word 'dowel' would probably fit, but projections already embedded in those parts. Most plastic things made of two or more parts have those, usually. Snap-together model kits, tapes, computer cases and the like. I edited my question for clarity; I also added new pictures. – Reddast Jul 16 '13 at 18:10
  • @batpigandme: I think a grommet normally has a hole in it, through which you can safely pass an electrical cable, for example. The grommet is normally plastic/rubberised, so there's no danger of the cable getting nicked by sharp edges of the original (larger) hole where you fit the grommet (in a pattress box, for example). I don't think grommets are ever used as fastenings. – FumbleFingers Jul 16 '13 at 20:22

Not sure that there's one word to describe all of those. I seem to recall (going back 50 years) that in the instructions for Airfix kits, they were called 'pips'

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