Ring size
The inside diameter of scope rings: 1 in (25.4 mm), 30, 34 or 35 mm. It must equal the scope's tube diameter. Many thermal scopes have a 30 mm tube; others take only their maker's mount.
What it means
Scope rings are sized to the scope’s main tube. The common sizes are 1 in (25.4 mm), 30 mm, 34 mm and 35 mm. A 30 mm scope needs 30 mm rings; there is no adjusting for a different size.
Thermal scopes split into two groups. Some have a round tube that takes ordinary rings (Pulsar’s Thermion 2 and AGM’s Adder, for example, use 30 mm). Others have a flat base or dovetail that takes only the maker’s own mount, such as a Picatinny clamp built onto the body.
What it changes in the field
- Choice. A tube-bodied thermal can use any ring maker’s 30 mm rings or cantilever mount, at any height.
- Fit. A proprietary base limits you to the maker’s mounts, and sometimes one height.
What to look for
- The optic maker’s figure. Use the tube diameter the scope’s maker publishes, not a dealer listing.
- Room on the tube. The rings need tube length free between the turrets or housing and the eyepiece. Thermal makers rarely publish it.
- Torque. Pulsar, for example, gives a maximum for its ring screws. Follow the lower of the ring maker’s and the scope maker’s figures.
How we use it on this site
Optic pages show the tube diameter only where we have checked the maker’s own page or manual. A mount whose rings equal that diameter is listed under “Interfaces match (calculated)”.