what is this thing?

What is this and what could it be used for? I found it under my car. It looks like a big plastic screw. Could it have fallen off of something for my car?

I really doubt it’s from an automotive application.

What size is it?

It looks like the screws that hold plastic trim on, like the engine covering, or stone guard.

It’s pretty big for a screw. Like 3 inches

Your photo isn’t very multi-dimensional :), but that was my thought, too.
(Google image search result)

did you find it screwed together like that? (it has two parts)


This is the correct answer. I have seen them used in my vehicle. They are used to secure a plastic part - some sort of trim or cover - to another, also usually plastic, part.

It has a slight resemblance to some automotive fasteners, but the way the two pieces fit together and most especially the size are something I’ve never seen on a car.

Here’s a typical [automotive trim retainer](http://i.ebayimg.com/00/s/MTAyNFg4MTQ=/$(KGrHqEOKpwE6VVTvq,jBOtZlDWJN!~~60_35.JPG). It doesn’t measure over 3/4" (probably closer to 1/2") in either diameter or length. I find it very hard to believe that a retainer that screws together just like the one the OP showed, or one that is 3" in any dimension, much less of both that design AND of that size can be found on any automobile.

Maybe it large because it holds a big piece. Like a plastic bumper part. Or a mud flap.
ETA anything hanging loose on your car?

Is it possibly an access plug, from the lower engine cover/shroud, for the oil drain plug?

No, no, …

and no.

I’ve been fixing cars professionally for over 45 years. That’s simply not the type of fastener they use.

I don’t know what it fits, but that type of fastener is called a “sex bolt”.


The mind boggles.

Perhaps from another, LARGER vehicle… like a UPS truck?

Might hold the front bonnet lining in place.

I have something similar holding down the spare tire in my trunk.

Seems to be a furniture assembly bolt for DIY things. Being found under a car does not mean it is from a car. Very light weight, many ways to get under the car from a long way away. IMO

I’ve seen those recently in toy packaging. They replace zip ties and wire ties. It’s usually when you have a heavier toy in a semi open cardboard display package.