bolts on harley davidson sport model

[Venus]

Can anybody help me with the bolts to mount the gastank and toolbox on a Sport model.
The directory of spare parts says it must be factory number B0525B.
A numerical list of bolts,nuts,washers,etc that I have got from Tom Wilcock tells me that it is a 5/16-24 x 9/16 Cap screw but I do not know what a Cap screw is.
I have a picutere of a bike in a dutch museum with special bolts.
Is this a Cap screw?
It is also used on all three speed models for the frame bracket.
It is also used on 1916 twins for thew rear cilinder clamp.
It is also used on 1915 all models for the rear mud guard brace according to my list.
Can anybody explain what a Cap screw is and where to get them.

[exeric]

A cap screw is a hex head bolt. Harley Davidson made their own hardware in the early days and they made their cap screws with slightly taller heads than the cap screw bolts you find today. Many people are forced to make their own hardware for early motorcycles.

[Chris Haynes]

If it is the same cap screw that attaches the tanks to the frame Colony has them.

[bill campbell]

Hey Venus a good place to check is competition dist .com . Lonnie supplies a lot of parts for pre 1930's hd's he's located on main st in Sturgis South Dakota has a high quality catalog does mostly single's and V twins but some of the stuff should interchange good luck billy

[Tommo]

The cap screws holding my Sport model tank on have heads that are 7/16 across the flats and the heads are 1/4 high.
The top corners of the Hex head are slightly rolled off.
I must emphasise that this is what is fitted to my bike and I don't know for sure if they are correct or not.
I tried a 1/2 AF bolt and with it things get pretty close so in my opinion the 7/16 AF is a better option which may or may not be correct
I've always thought that "Cap screws" are fully threaded where-as bolts have a portion of the shank that is not threaded.

[Tommo]

Louie,
You've got a nice original Flat Twin, what are the bolts like that hold your tank saddles on?

[LouieMCman]

I'm up in Michigan at the 71st annual Motor Maids convention but I'm pretty sure the bolts are hex head slightly rounded corners like Tommo discribed, the picture in the museum doesn't look right. I'll look next week when I get home.

[MMasa]

Tommo is correct. A cap screw is threaded its entire length less the head obviously.
Mark Masa