4 Pcs Linear Rail Shaft Collar 12mm ID 30mm OD 10mm Thickness Aluminum Alloy Shaft Limit Fixing Ring with M4 Screw 1[Shaft Fixation] These shaft collars are used for linear rail shaft fixation and positioning, ideal for DIY CNC machine tools. Featuring 12mm inner diameter, 30mm outer diameter, 10mm thickness. 2[Seamless Integration] Designed to perfectly mesh with the shaft, this linear rail stop collar ensures easy installation and a tight fit, enhancing stability. 3[Secure Fastening] Equipped with a M4 fixing screw, the limit fixing ring securely clamps onto the shaft without causing damage, providing reliable and stable fixation. 4[Aluminum Alloy Made] Crafted from aluminum alloy, this shaft stop collar is lightweight yet sturdy, not easy to be broken or damaged. 5[Corrosion Prevention] Its surface is resistant to oxidation and corrosion, ensuring long lasting performance even in demanding environments.