Ensure leak-free pipe connections with our 6-piece Brass Pipe Cap Set! These 1/4" NPT Female threaded caps come with rubber gaskets for a secure, airtight seal, making them perfect for plumbing, gas lines, compressed air systems, and hydraulic fittings. IMPORTANT SIZE INFORMATION Thread Type: 1/4 Inch NPT (National Pipe Thread) – this is the STANDARD thread size this cap fits Actual Cap Inner Diameter: 13mm / 0.51 inches (this is the INSIDE opening of the cap) Actual Cap Outer Diameter: 17mm / 0.67 inches (this is the WIDTH of the cap body) Actual Cap Height: 9mm / 0.35 inches Please note: The "1/4 inch" in the product name refers to the NPT thread standard, NOT the physical diameter of the cap. Many first-time buyers expect a 1/4-inch (6.35mm) cap and receive a 13mm cap – please check your measurements before ordering!