Caps, Grips, and Closures

Caps, grips and closures are protective devices for the ends of a shaft, tube, pipe, fitting, connector, screw, bar, or other shape. They can also be used to provide a hand grip or hanger tip. Caps are available in many different shapes and materials.  Common shapes include round, square, rectangular, round handle or hand grip, flat handle or hand grip, hex cap, “U” shape cap, “I” shape cap, 90° angle cap, screw cap or plug, and washer cap.  Common construction features include threaded, tapered, and anti-roll.  Threaded caps have a female thread.  The thread can be straight or tapered (NPT).  Caps have a female thread and plugs have a male thread.  Tapered caps and plugs have tapered sides, providing a snug fit.  Some can be used as either a cap or a plug.  Tapered caps and plugs are versatile and can be used for straight tubes and bars, male and female NPT threads, and male straight threads.  Anti-roll caps are round caps with a square end to prevent tube or shaft from rolling.

Important specifications to consider when searching for round caps, grips, and closures include NPT size, BSP size, and diameter.  The NPT size option applies to round caps only where the object to be capped has a male NPT (National Pipe Thread) thread.  The BSP option applies to round caps only where the object to be capped has a male BSP (British Standard Pipe) thread.  The diameter dimension applies to round caps and plugs only.  For straight threads the major thread diameter is the most important (for example: .25 for a ¼ straight thread).  This dimension is not considered where cap/plug or object being capped/plugged has a tapered (NPT or BSP) thread.  Common round cap features include flange, knurled or faceted head, slotted head, retaining head, and tear tab.  A flange is included for easy removal or additional protection of bearing surfaces.  They also prevent accidentally pushing the plug all of the way through the opening.  Knurled or faceted heads are usually found on threaded caps and plugs only, knurls or facets allow easier installation and removal, either by finger or wrench.  Slotted caps and plugs can be installed or removed with a screwdriver.  Retaining rings fit over the object to be capped and function to keep the cap in place during servicing.  Caps with a tear-tab or strip are easily removed.  When the tab is pulled the cap tears away, once removed they cannot be reused.  Important dimensions to consider for square or rectangular caps, grips, and closures include width and length.  The width is the smaller cross sectional dimension for rectangular caps or plugs.  If the section is a square, the width and length is the same dimension.  The length is the larger cross sectional dimension for rectangular caps or plugs.  If the section is a square, the width and length is the same dimension.

Common materials of construction for caps, grips, and closures include aluminum, Delrin, EVA, Monel, nylon or polyamide, paper, polyetheretherkeytone (PEEK), polyethylene, polypropylene, silicone rubber, styrene butadiene rubber (SBR), stainless steel, and vinyl.  Additional features to consider when searching for caps, grips and closures include hanger tips, lift or pull tabs, and venting.  A hanger tip allow for the hanging of tools or other items.  Hanger tips are sometimes integrated with handles or grips.  Caps can have a tab or ring for easy removal or plug is of pull plug construction.  Pull plugs are designed for "through-hole" applications.  They use a smaller diameter "pull section" to pull the plug until it is snug in the hole.  Vented caps are commonly used in the medical industry.  The vent allows airflow during gas sterilization and prevents the cap from blowing off during extreme heat conditions.