The bearings are a little better in the V:
"Many of the component parts of the Series IV are similar, if sometimes less rarefied, to those in the V. For example, bearings of ABEC-3 tolerance are used instead of ABEC-7."
This link has a pretty detailed difference list:
http://www.sme.ltd.uk/content/Series-IV-1342.shtml
"Many of the component parts of the Series IV are similar, if sometimes less rarefied, to those in the V. For example, bearings of ABEC-3 tolerance are used instead of ABEC-7."
This link has a pretty detailed difference list:
http://www.sme.ltd.uk/content/Series-IV-1342.shtml