Design Würth Screws to Eurocode 5

Würth manufactures fastening and assembly technology from Künzelsau, Germany, and the Würth Group operates in 80 countries. Its ASSY series of structural wood screws is made for timber construction in solid timber, glulam, CLT and LVL.

Thirty-one families are integrated for the EU region, all under ETA-11/0190: 5 to 14 mm diameter, 20 to 1500 mm length, service classes 1 and 2, with service class 3 on the zinc-nickel plated and highly corrosion resistant stainless families. Characteristic values are read from the database at calculation time, not interpolated.

• ASSY 4, carbon steel (13): countersunk with milling pockets or milling ribs, zinc-nickel countersunk, washer head and washer countersunk head, combi hex and hex head, underhead thread, joist hanger head, and the Isotop cylinder head.
• ASSY 4, stainless steel (6): A2 countersunk, A2 countersunk with milling pockets, A2 washer head, and countersunk screws in grades 1.4529 and 1.4539.
• ASSY plus 4 (5): countersunk with milling pockets, A2 countersunk with milling ribs, two A2 terrace heads, and the A2 large truss head solar screw.
• ASSY plus VG 4, fully threaded (7): countersunk, cylinder and combi hex heads, with and without milling pockets, and the 14 mm external Torx screw, the only one reaching 1500 mm, at a yield moment of 86 Nm and a tensile strength of 62 kN.

• Solid timber, glulam, CLT and LVL.
• Steel-to-timber connections.
• CLT face and edge fixing.
• Insertion at an angle to the grain.
• Timber reinforcement, on the 14 fully threaded families marked for it.
• Service class 3 on the zinc-nickel plated and 1.4529 / 1.4539 stainless families.

• Compression screws are verified against buckling: the design axial capacity of ASSY plus VG and fully threaded ASSY screws is the lesser of the resistance against pushing in and a buckling resistance on an elastic foundation, at a characteristic yield strength of 1000 N/mm².
• Reinforcement is assessed in three modes: compression perpendicular to the grain at 45 to 90 degrees, tension perpendicular to the grain at 90 degrees, and shear reinforcement, limited to 8 mm fully threaded screws driven at 45 degrees, at least four in a line.
• CLT edge surfaces have their own design basis: an embedment strength of 20/√d and a withdrawal capacity of 20 d^0.8 lef^0.9, both independent of the grain angle, with edge spacings of 10d and 4d and a minimum penetration of 10d.
• Embedment strength varies with the insertion angle: the certificate divides the Eurocode expressions by (2.5cos²α + sin²α), where α is the angle between screw axis and grain.
• Beech LVL and FST carry a withdrawal parameter of 35 N/mm² in the integrated data, against 10 to 12 N/mm² for softwood, softwood LVL and CLT.

All Würth screws on this page are available in the Screw module, in the connection detail calculators for panel-to-panel joints (half-lap, spline and butt joint), slab-to-wall, wall-to-wall, floor-to-wall, and in the rib-deck calculator for flexible connection design.
The 14 families marked for reinforcement in the database also appear in the reinforcement connection details: beam notch, beam penetration, and beam compression perpendicular to grain.

Design follows EN 1995-1-1 clause 8.7, with 8.7.2 for axially loaded screws, and both the 2004 and 2025 editions are supported. Clause 8.7.2(1)P lists buckling under compression among the failure modes without setting a rule for it; ETA-11/0190 supplies one in Annex 2. It was issued supporting CE marking. The same product data is used for design in the AUS and NZ markets in accordance with the applicable design standards there.