Screwdriver Bit PH Halfmoon 4 mm, Wera 851/9 C PH, length 44 mm

The Wera Screwdriver Bit PH Halfmoon 4 mm (model 851/9 C PH) is a single precision bit intended for use with compatible bit holders, manual drivers, and power tools that accept standard bits. The bit features a Phillips (PH) halfmoon geometry with a 4 mm tip diameter and a 44 mm overall length, providing accurate engagement with PH fasteners and reliable torque transfer for assembly, maintenance, and repair tasks.

Advantages

The halfmoon profile ensures stable seating in Phillips screw heads, reducing cam-out and wear on both screw and bit. Manufactured by Wera to standard quality specifications, the bit combines consistent dimensional accuracy with durable material properties for repeated use. The 44 mm length offers a balance between reach and control, suitable for confined spaces while remaining compatible with common bit holders and driver adapters.

Suitable for (tasks / use cases)

• Assembly of furniture and fixtures with Phillips fasteners
• General maintenance and repair work on appliances and equipment
• Light to medium-duty mechanical fastening where standard PH bits are used
• Use with manual bit holders, ratchet handles, and powered drivers

Key specifications

• Tip type: Phillips (PH) halfmoon profile
• Tip diameter: 4 mm
• Overall length: 44 mm
• Compatibility: standard 1/4" hex bit holders and drivers
• Typical material properties: hardened tool steel with corrosion-resistant finish (manufacturer standard)

How to use

Insert the bit securely into a compatible 1/4" hex bit holder, manual driver, or powered driver. Ensure the tool is set to the appropriate torque and rotation direction for the fastener type. Engage the bit with the Phillips screw head so the halfmoon profile seats fully before applying torque; this helps minimize slippage and preserves both bit and screw. After use, store the bit in a holder or case to protect the tip from damage.

Usage recommendations

For best results, match the bit to the correct Phillips screw size and avoid excessive torque settings that can deform the screw head. Inspect the bit tip for wear before use and replace it when the profile shows rounding or damage to maintain reliable engagement and safe operation.