Proto J4990-4MST Hand Hex Bit Socket 3/8 in Drive 4 Mm

Product Description

The PROTO J4990-4MST is a hand hex bit socket designed for 3/8 inch drive ratchets and wrenches. It accepts a 4 mm hex bit and delivers reliable torque transfer in tight or confined fastener locations. With an overall length of 1-49/64 inches and a bit length of 3/4 inches, this socket is built for precision work on hex-head fasteners in HVAC equipment, plumbing fixtures, electrical enclosures, and general mechanical assemblies. Licensed tradespeople and experienced DIYers use this socket where a standard hex key cannot generate adequate torque or where a ratcheting drive is preferred for speed and control.

This hex bit socket is suited for residential and commercial service applications where 4 mm hex fasteners appear on equipment panels, access covers, valve stems, motor assemblies, and similar components. The compact overall length makes it practical in moderately restricted spaces without requiring a deep-well socket. It is sold individually and is compatible with any standard 3/8 inch drive ratchet, extension, or torque wrench.

Key Features

• 3/8 inch square drive fits standard ratchets, extensions, and torque wrenches
• 4 mm hex size for metric hex-head fasteners
• Bit length of 3/4 inches for positive fastener engagement
• Overall length of 1-49/64 inches for use in moderately tight spaces
• Lightweight at 0.09 pounds for reduced hand fatigue during repetitive fastening

Compatibility

Designed for use with any standard 3/8 inch drive hand tool including ratchets, breaker bars, and torque wrenches. Fits 4 mm hex fasteners as found on a wide range of mechanical, HVAC, plumbing, and electrical equipment components.

Installation Notes

This socket is installed and used by technicians and mechanics working on equipment requiring 4 mm hex fasteners. Always ensure the drive tool is rated for the torque required by the fastener application. Inspect the socket for wear or rounding before each use, and replace if the hex geometry shows deformation. De-energize or isolate equipment before servicing fasteners on live electrical or pressurized assemblies.