Product: Left Hand Threaded Bolt (2 pcs) Main color: Black Material: 40Cr steel Strength grade: 10.9 Why choose these bolts Correct orientation for reverse-rotation or anti-loosen applications: the left-hand thread prevents components from unscrewing where standard right-hand bolts would loosen under rotation or torque. Strong, reliable fastenings: made from 40Cr steel and rated 10.9 for high tensile strength and wear resistance in demanding assemblies. Flush, clean installation: countersunk (flat) head sits flush with the surface for a neat finish and reduced snagging. Secure drive and precise torque: hexagon socket drive accepts a 3.1 mm hex key for controlled tightening without cam-out. Versatile, adjustable engagement: fully threaded M5 shaft gives full-length engagement and fine adjustment where needed. Key specifications Package: 2 pcs left-hand threaded bolts Thread size: M5 (fully threaded) Total length: 20 mm / 0.8 inches Head shape: Countersunk / flat head Head diameter (D): 9.6 mm / 0.38 inches Drive type: Hexagon socket Hex socket width: 3.1 mm / 0.12 inches (compatible with 3.1 mm hex/Allen key) Material: 40Cr steel Strength grade: 10.9 Weight: 7 g (per bolt) Color: Black Practical use scenarios Machinery and rotating equipment: use where shafts, pulleys, or couplings rotate counterclockwise relative to the fastener and a left-hand thread prevents self-loosening. Automotive or drivetrain assemblies: secure components on the reverse-rotating side where a left-hand thread is specified to maintain clamp force under torque. Fixtures and repairs requiring a flush finish: countersunk head provides a low-profile installation on panels, brackets, or assemblies where clearance and appearance matter. Notes on fit and installation Confirm M5 thread and 20 mm length suit your application before installation. Use a 3.1 mm hex key for installation; apply appropriate torque for 10.9-grade fasteners. Supplied as a pair (2 pcs) in black finish. This bolt is a direct, specification-accurate choice when you need a durable left-hand M5 fastener with a flush countersunk head and hexagon socket drive.