The ultimate in sight picture "High End" polished glass inserts have no bar or cross-hair. They feature a fixed ring diameter, available from 3.0 to 7.5mm in 0.1mm increments, with ring thickness available from 1.0 to 1.4mm in 0.1mm increments.
We try to keep most diameters from 3.6 - 5.0 in stock, in every width. The narrower ring widths are by far the most popular - 1.0 and 1.2 especially.
These are also available with coloured glass in red, blue or yellow, for increased contrast in your sight picture.