The black ring sight is called the United States Secret Service Sight (USSS) or the USG sight. The black ring sight functions much better than the white ring sight in that you can see the black cross-hairs against white backgrounds; however, you cannot see the cross-hairs against black backgrounds or in low light conditions. The Rem-T3B solves this problem by illuminating the internal tritium sight.
The Rem-T3B is essentially the same design as the Rem-T3, except the LED is shaped to fit the underside of the black ring sight. The Rem-T3B needs to be permanently attached because there is no light-collecting well for the LED to reside in. There needs to be a minor operation that needs to be done to the underside of the black ring sight to fit the LED (see installation video below). It is a semi-delicate procedure which I offer to do for free. You may decide to do this yourself, but it is not recommended.
The Reticule Enhancement Module T Bar 3B (REM T3B) fixes the problem that is inherent in the Black Ring Sight of the P90/PS90 Black Ring Sight Weapons System. In certain low light conditions, or when aiming at dark or black colored backgrounds, the Ring Sight loses its sight picture. When that happens, just turn on the REM T3B and the Reticle will be bright and clear.
The REM T3B has 11 illumination settings, so the T bar can be seen outdoors in daylight on its brightest setting or in total darkness on its lowest setting. The REM T3B does not interfere with the Tritium illumination of the Ring Sight.
The REM T3B fits in the sling well just under the Ring Sight. It is ambidextrous, so it can be mounted on the left or right side of the rifle.
The REM T3B uses one CR2032 3-volt battery (included.) The battery life depends on the color and ranges from 182 (Green) to 390 (Blue) hours of continuous use. Red has 220 hours of continuous use.
The REM T3B comes with a 30-day money-back guarantee. If you are dissatisfied with it, please send it back to me, and I will give you a full refund (minus shipping costs.)