I don't think you fully understood the posts above relating to steerer tube diameter and threaded v. threadless. I would reread them.
What do I need read in order to understand ? The dimensions I have, I can't find conversions for ?
Hoped someone here, who has a lot of experience might just easily say what I need.
It's a threaded headset, I am looking for a quill with 'a removable face plate' as stated by 'CACycling'
but from the sizes I have, what stem do I need to look for ? What size probably is the quill stem already installed, which is ( 7cm/2.8" ) and what size are the handlebars, which in the centre are ( 8.3cm/3.25" )