Best resource to lookup fastener sizes

New member here and hope this is the correct place to post this. If not, feel free to move it.

I am NOT a gifted mechanic although I have been working on my own motorcycles for eons. I often run into situations where I need to replace a fastener (or have difficulty removing one) and it would be VERY helpful to know precisely what's in there. I do have a parts catalog but it does not provide head type/size, thread pitch and so on. I'm currently getting ready to pull apart my rear caliper and it's not clear what socket to use on the pad retaining pin. Seems to be a 12 point 1/4" bolt (service manual says it's metric) but the socket fit is a tad wobbly. 6mm is too small and 7mm is too big. I'm concerned about rounding off the head if it doesn't want to come off easily.

This is more of a general question on how to lookup the dimensions of R&R parts than it is about this specific bolt. It would be great if the HD parts catalog included this info but.... with a fastener of this type I don't know how I could even precisely measure the head.

Thanks very much in advance!
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I not much of a Torx fan especially on the smaller sizes where if you wobble the wrench it will destroy the fitting. I have replaced as many as possible with stainless steel hex head deep seat.
This is when after years of buying SAE tools than the metrics invasion comes into play followed by the bad dream that brought us torx bit and sockets followed by tamper proof and metric with 1/2 size comes in handy.
The head on the pin you are questioning is a "Torx", 12 point sockets work, but not a precise fit.
Oh great.... another tool set I need to buy :(

So not being a gifted mechanic, are there SAE and metric E-torx tools or just one standard that fits all? Amazon has a set for $16 that will probably work for me and the E-7 looks to be about right which would imply metric. I have no idea what the number after the T refers to.... perhaps just an arbitrary numbering assignment scheme? The things I don't know stagger the imagination.

Needs to be a thin wall socket as the head is mostly recessed and the OD of the socket also needs to be thin as the swing arm frame leaves very little clearance to attach the socket straight on. The torque spec is not very tight so I may be able to get the pin out with the caliper removed but I don't want to wait until it's off the bike to find out this isn't true. I'd really like to be able to remove the pin, inspect it, lube it and see if that fixes my problem before getting in deeper.

So of course I very much appreciate the info. You actually solved two problems... the first being that I didn't even know what kind of fastener it was. -1 to me for being a dope. So other than being a genius which you clearly are, how would a mere mortal know that this was an E-torx and not a 12 point bolt and more importantly how would anyone know what size E-torx it is? How could I even measure it? This information has to be out there somewhere. One would think that it would be in the uber-expensive MoCo service manual that has always been of poor quality. I use the Cylmer which has much better illustrations and usually easier to follow instructions but neither say a word about what kind of fasteners they are. I've watched numerous youtube videos on brake rebuilds and no one has mentioned that this is a torx but a few have mentioned the torque spec.

As I said, my purpose for posting was to find out what resources were out there to obtain information on fasteners generally. I've had several cases where I knew what I was removing would need to be replaced but I could find no information on thread diameter and pitch. I do know how to measure things like that but I can't have my daily driver out of commission for a week or two waiting on a replacement bolt!

I agree with another on here and the first thing I looked for was a replacement set of pins that have decent heads. There's a nice Westcott aircraft quality hex head set for my front calipers but unable to find anything in stock for the rear.

Very much appreciate the info. Thank you!