Sport-Thieme Spring Locking Collars for Weight Bars – attach, change weight plates, continue training. The Sport-Thieme Spring Locking Collars for weight bars are quick-release clamps that allow you to easily change and secure weight plates on the barbell. They require minimal time, enabling you to quickly resume your workout. The collars fit all weight bars with a diameter of 28 mm, 30 mm, or 50 mm. The versions for 28 mm and 30 mm also feature plastic handles. Product type: Spring closure • Bar diameter: 30 mm.