Recognize this bolt?
 

Found this bolt laying in the underside engine cover of my E300D when I took it off during a B service. No one but me has worked on my car and I don't remember dropping one, but I must have. Anyone recognize what this bolt might be for?

It's a self-tappng screw that could have been used to secure something to an inner fender or firewall. Check all around the engine bay for something missing a screw, especially on the lower part where it would be easier to miss.

I don't think MB used that type of bolt.

anything aftermarket put on the car?

I've a few like that on my W201 - they are indeed as Jeremy suggests the type that fit into bodywork.

Hmm

all the body bolts on my 87 190D have the narrow point, or a starter point... none are notched like that. (and I've had the entire front end pulled apart... but my cars are all 87 or older. who knows what the bean counters at MB approved later in production.:mad:

My W201 is of a 1992 vintage if that helps us narrow down the bean counter effect!

Self tapping bolts are used on low stress applications and that type needs a through hole to expel chips.

As others have said, firewall but also have a look at injector line clamps or other thickish sheet metal items. Have a look at the head stamping and compare to other bolts, there is a chance this bolt was dropped and another put in it's place.

What is the bolt head MM?

I would not worry too much about it.

As per Jeremy's comments, self tapper - is that a captive washer?

I'm not quite sure what you mean - Captive washer or captive nut?

Probably not!

Self tapping bolts / screws go into a hole that has not been tapped - the screwing in of the bolt or the screw makes the threads (not that you'd really be able to call then threads - more like deformations).

(I hope this helps)

Yup, captive washer although I may have just have invented that terminology :)

Basically the washer is held in place by a small recess under the bolt head.

I can have a look at mine to see if there's anything that looks obvious.

too bad we don't have access to any database that could show us the various uses of hardware with a certain diameter, pitch, head, etc. on the chassis.

at least you can avoid searching in places where the screw would not have fallen into that cover.

the fact that it's self-tapping is surprising to me since i don't remember seeing any such screws on my car. did MB really use ST screws in factory models? if you showed the markings on its head we might know more.

How about the bolt that keeps the inner sway bar brackets at the frame in place?

http://www.w124performance.com/image...r_brackets.jpg

Type 23 Screw. Body Fastening

Which have a slot milled along the shank point. This will cut a thread in soft metals and hard plastics. Also used to remove paint from threads of captive nuts on painted panels, eg: automotive