Sorry, miss quote..
The 10 is a .75.
Again there is not allot of point going for the specific thread pitch unless Tap co already have everything set up. That will make the cost of the T&D's much cheaper in the long run as set up costs are the big contributing factor. So you may well find that you are pushed towards them.
The only main talking point is in the double or triple starts really. I have both and TBH the triple feels nicer and easier to cap than a double but the double does the job. If that makes sense.
The pitch difference between 0.5, 0.8 and 0.75 wont be noticed by the end user. Just how anal the pen maker wants to be. 
I may be wrong but I understand that most kit suppliers supply double thread fittings for the cap and postable.
So in my view the fine thread is right but it wont matter to the end user. the coarse thread (1.25 and above) doesn't look nice on a quality pen in my view so stick to fine thread.
I have seen a pen maker talking to a potential customer all about the thread, triple start and all the techie stuff that the person walked away.. They don't need it.. simple.
Having said all the above my thoughts are that a thread can be made of any type the pen maker wants to be, it does't have to be any of the above, provided it does the job and screws the cap and body together the end user really isn't bothered.
I have used a standard off the shelf 10 and 12's x 1.5 pitch, looked not bad and did what the customer wanted.
The only area you need the specifics is when using the nib fittings from suppliers... That is the only time you will truly need specialized threads.
