Coastal Pet Circle T Oak Tanned Leather Round Dog Collar Circle T Oak Tanned Leather Round Dog Collar. Collar: tan. Width: 5/8", adjustable sizing to fit necks 11.5" to 14". Made of full grain, top quality leather that has been vegetable tanned. The round collar has a leather core to ensure that they hold their shape and is rounded over lengthwise, expertly sewn together. The perfect choice for long-haired dogs or dogs with sensitive skin. Great alternative to nylon.