The NAS561P4-18 is a National Aerospace Standard (NAS) slotted spring pin (often referred to as a roll pin) used for precision alignment, retention, and vibration-resistant fastening in aerospace and aviation assemblies. It is designed to provide a flexible, self-retaining interference fit inside a drilled hole without requiring threads or additional locking hardware.

This specific configuration corresponds to the NAS561P4 series with a nominal diameter of 1/8 inch and a length of 1-1/8 inch. The slotted tubular design allows controlled radial compression during installation, creating spring tension against the hole walls to resist loosening under vibration and cyclic loading.

It is widely used in aircraft structures, engine accessories, control linkages, and mechanical assemblies where lightweight, serviceable retention pins are required.

Key features include:

NAS (National Aerospace Standard) slotted spring pin / roll pin
Nominal size: 1/8" diameter × 1-1/8" length
Self-retaining spring tension design (no threads required)
High resistance to vibration loosening in aircraft environments
Manufactured from hardened spring steel (typically 1070–1095 carbon steel range)
Cadmium-plated or corrosion-protected aerospace finish (depending on variant)
Used for alignment, hinge retention, and mechanical locking applications
Lightweight alternative to solid dowel pins or threaded fasteners
Designed for precise hole interference fit (controlled compression slot)
Conforms to NAS561 aerospace standard requirements
Common in general aviation, military, and OEM airframe assemblies
Replaceable during maintenance without damage to surrounding structure