Hi Mark,
I think most of us received Ketan's nice Catalogue for his business, Arceurotrade. Page 14 lists ER Collet nuts with ball bearing . Benefits include reduced friction = higher clamping pressure, easier to use especially closing a collet down to smaller end of its range and compatible with T2 type nuts.
He lists a type M mini collet nut, up to 6mm dia. smaller than A or T1 but no mention of UM so don't know what you mean by UM.
ER32 type T2 (plain) ?6.80. Ball bearing type B also ER32 = £7.60. This is typical price difference. Save time go on the website and get what you want.
Good luck,
John
Edited By JasonB on 16/10/2016 07:40:40