Don't get any plastic collars. Full metal only. Ivanko COT collars or any York style Spin lock.
Amazon.com : 1.25 lb. Chromed Training Collars (Pair) : Exercise Wraps : Sports & Outdoors
Amazon.com : Olympic Bar Collars (Pair) (Spin Lock Collars, 2") : Exercise Weights : Sports & Outdoors
York Barbell Olympic Collars | eBay
Vintage "York Style" Olympic Barbell Hvy Duty Spin Lock Collars | eBay