Holland's Scope Level 30mm (tube size) . They are machined from 7075-T6 aluminum and hard black anodized. These scope levels are without a doubt the most attractive, well designed level you can buy. They feature a hole for attaching your data card to the rifle. Most importantly they can be seen from a firing position, say goodbye to "turkey necking" to check for reticle perpendicularity. Available in 1", 34mm.