Question about washers; not clothes, but hardware.

[Molly Brown]

Why is the hole of a =BC=94 fender washer =BC=94 but the hole of a =BC=94 c= ut washer larger than 5/16=94?.

[aemeijers]

Um, lessee- what is a plausible made-up answer for this? Fender washer (as the name implies) is so the bolt won't draw through the substrate, so you want a tight fit, where the bolt can't pull through the washer. Regular washers, you want them to be able to move around a little so as to act like a little bit of a bearing when things flex? They can also deform a little when tightened, to seat better.

IOW, hell I dunno. But now you have me curious. Where are our resident Actual Engineers? I've only used fender washers with self-tapping bolts and machine screws, not through bolts with nuts. (And it was usually on actual fenders and other car body parts, to refasten through wallowed-out holes in sheet metal.) I guess the washers for carriage bolts fall somewhere in the middle- I remember them as being a pretty tight fit, but they are smaller than fender washers.

[DD_BobK]

Actual washer dimensioning can be all over the map.

SAE washers are typically 1/32" larger than the nominal bolt size. Aerospace washers can be be very closely sized to the nominal bolt size (like .510" for 1/2" bolt)

The cut washers you're seeing with greater than 5/16" hole is a so- called 1/4" are probably junk imports.

Hardware buyers, unless controlled by some sort of spec, buy some pretty crappy stuff. QC can be close to non-existence and the original design intent lost. :(

In my experience, for decent hardware, +1/32" is a good oversized hole for a bolt, anything more is just plan too sloppy.

Maybe I didn't fully understand the point of your question.

cheers Bob

[Larry Fishel]

My WAG would be that since fender washers are intended to be used with screws with "conical" heads, the slightly larger hole allows for the portion of the head between the substrate and the "outer" edge of the washer. Otherwise they'd have to bevel the hole...

[Tony]

I wish I knew the answer, it bothers me also that normally a washer of the next smaller size fits nicely on the next size larger bolt.