Wiktionary
n. a small metal ring on the side of a firearm, allowing it to be hung on a saddle hook or attached to a lanyard.
Wikipedia
A saddle ring is a metal ring attached to the receiver of a rifle or carbine allowing it to be tied to a saddle or used with a special sling. Saddle rings could be attached directly to the firearm, or in some cases to a saddle ring bar, which allowed the saddle ring to slide along the action, such as on the British Enfield P1856, a short cavalry version of the Pattern 1853 Enfield used in the American Civil War. Virtually every carbine-sized weapon used in the Civil War was equipped with a saddle ring and/or saddle ring/bar. Saddle rings are most commonly found on lever action rifles and other firearms of the late 19th and early 20th centuries that were suitable for use on horseback. The muzzle of the rifle was placed in a carbine socket or boot. The idea behind using the saddle ring, and its carbine sling, is to allow the mounted soldier to never be separated from his weapon.
Usage examples of "saddle ring".
The racing harness, like the common tarn harness, works with two rings, the throat ring and the main saddle ring, and six straps.
Even after I had drawn her to the saddle before me and belted her securely to the saddle ring, I had to force her fingers from the rung of the mounting ladder.
He bent across my body and I felt my crossed wrists lashed to a saddle ring.
As swiftly as I could I then explained to him the guidance apparatus, the main saddle ring and its six straps.
Jecks bent over and extracted the travel biscuits from the bag tied on the left saddle ring, offering her one.
She had been left a length of cord between her lashed-together wrists and the saddle ring to which the rope was knotted, and if she lifted her hands and bent, she could just scratch her nose.
These pass from the throat strap to the main saddle ring, which is fixed on the saddle.