Teslong 5-Mirror Set
This set includes one of each diameter side-view mirror:
0.2 in (5 mm)
0.23 in (6 mm)
0.27 in (7 mm)
0.33 in (8.5 mm)
0.39 in (10 mm)
This kit allows you to see more of the lands and grooves inside of large-caliber rifle barrels than you would with just the standard 0.20-diameter mirror.
These mirrors also help keep your borescope centered inside the barrel and thus maintain a more consistent focus as you rotate the borescope probe.