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Westfield Fasteners Product Specification:

NF E 27-128 - Double Slotted Mushroom Head Screws

This product guide contains the specification for metric double slotted mushroom head machine screws, a series of standard parts available from Westfield Fasteners. This specification is based on the French national standard NF E 27-128.

Product Description

Double slotted mushroom head machine screws manufactured to NF E 27-128 feature a wide, low-profile head that provides an increased bearing surface compared with conventional pan head screws. This makes them particularly suitable for fastening softer materials or applications where the clamping load needs to be distributed over a larger area to help reduce the risk of surface damage.

The double slotted drive is compatible with standard slotted screwdrivers, while the machine thread is intended for use with a matching internally threaded component or nut. These screws are manufactured with a full thread as standard.

Double slotted mushroom head machine screws are sometimes referred to as roofing bolts in certain industries, although the term "roofing bolt" is used for several similar fastener designs.

Figure 1 illustrates the principal dimensions of the screw, while Table 1 details the dimensional requirements and tolerances specified by NF E 27-128.

Figure 1: Double Slotted Mushroom Head Machine Screw

Table 1: Dimensions & Tolerances (mm)

Thread Diameter, (d)	Thread Pitch, (p)	Head Diameter, (dk)		Overall Head Height, (k)		Slot Width, (n)		Slot Depth, (t)
		Max.	Min.	Max.	Min.	Max.	Min.
M4	0.7	10.00	9.00	2.20	2.00	1.51	1.26	1.00
M5	0.8	12.50	11.50	2.70	2.50	1.51	1.26	1.20
M6	1.0	15.00	13.50	3.30	3.00	1.91	1.66	1.50
M8	1.25	20.00	18.00	4.40	4.10	2.31	2.06	2.00
M10	1.5	25.00	23.00	5.50	5.20	2.81	2.56	2.40

Typical Applications

Double slotted mushroom head machine screws are commonly used where a large bearing surface is required, including electrical equipment, sheet materials, light fabrications, enclosures, furniture and general engineering assemblies. The enlarged head helps distribute the clamping force over a greater area than conventional pan head screws.

E&OE