The rings are being used to fit a heavy 3-12x42 scope to a .177 (4.5 mm) air gun and until now, after some hundred shoots, it's working well. The scope is tightly fixed in the rings, however, the bases still moves even when locked in place by the gun's rail. It happens due to the heavy weight of the scope; therefore, these rails are best suited for lighter scopes. Yet it works very well, but recalibrations is required from time to time until the scope becomes fixed in place. It arrived in a small box with two pairs of spare rings and an hex screwdriver to fix the rings. Be aware that for better precision, the rings must be fitted simetrically, adjusting all the eighth screws with care. In overall, I'm satisfied with the purchase.
Looks good. Have not used yet