"The collar has four common purposes, Master," she said.
"First, it visibly identifies me as a slave, as a brand might not, if it should be covered by clothing. Second, it impresses my slavery upon me. Thirdly, it identifies my master. Fourthly-fourthly-"
"Fourthly?" he asked.
"Fourthly," she said, it makes it easier to leash me."
p80, Explorers of Gor

The Common Gorean Slave Collar

"The common female slave collar on Gor has a seven-pin lock. There are, incidentally, seven letters in the most common Gorean expression for female slave, Kajira."
p 294 Raiders if Gor

Plate Collars

"When the smith arrived, he took, from a rack in the wall, two narrow, straight bars of iron, not really plates but narrow cubes, about a half inch in width and fifteen inches in length. The girls were then motioned to the anvil. First Virginia, and then Phyllis laid their heads and throats on the anvil, heads turned to the side, their hands holding the anvil, and the smith, expertly, with his heavy hammer and a ringing of iron, curved the collar about their throats; a space of about a quarter of an inch was left between the two ends of the collar; the ends matched perfectly; both Virginia and Phyllis stepped away from the anvil feeling the metal on their throats, both now collared slave girls.
p 153-4 Assasins of Gor

Turian Collars

"The Turian collar, on the other hand, fits more loosely, and resembles a hinged ring, looped about the throat. A man can get his fingers inside a Turian collar and use it to drag the girl to him. It does not fit loosely enough to permit its being slipped, of course.
p251-2 Slave Girl of Gor

Rope Collars

"If I collar you," he said, "you are again a slave." "Collar me, Master," she said. Thurnus wrapped the rope twice around her throat, and knotted it.
p 240 Slave Girl of Gor

Beaded Collars of the Red Savages

"The red savages do not use steel collars. They usually use high, beaded collars, tied in the front by a rawhide string Subtle differences in the styles of collars, and in the knots with which they are fastenedon the girls' necks, differentiate the tribes.
p102 Savages of Gor