Design Bi-Mirth BM Quick Drill Screws to Eurocode 5

Bi-Mirth Corporation manufactures self-tapping timber construction screws at its plant in Taichung, Taiwan. The BM Quick Drill range is covered by European Technical Assessment ETA-12/0471, issued on 7 July 2025 under, replacing the version of 16 October 2023.

The integration presents the six BM Quick Drill families assessed under ETA-12/0471, grouped by thread type. Full characteristic design values are read from the Bi-Mirth database and applied at calculation time, not interpolated, so no per-article numbers are printed here.
Partial and full thread: BM Quick Drill, BM Quick Drill +, BM Quick Drill II, BM Quick Drill III

• Self-tapping screws with countersunk, wafer, pan, cylinder, washer and hexagonal heads, with or without a drilling tip, integrated at 6, 8, 10 and 12 mm in lengths of 40 to 600 mm.
• Carbon steel across the range, and stainless steel in A2 and A4 grades at 6, 8 and 10 mm.

Double thread: BM DT Quick Drill

• Countersunk, wafer and cylinder heads in carbon steel, 6 to 10 mm, in lengths of 65 to 600 mm.

Full thread: BM FT Quick Drill

• Countersunk, wafer, cylinder, hexagonal and hex washer heads in carbon steel, 6 to 14 mm, in lengths of 100 to 1500 mm.

Six families are integrated for the region, spanning 6 to 14 mm and 40 to 1500 mm.

At a glance, the Bi-Mirth families support:

• Solid timber, glued laminated timber and glued solid timber in softwood.
• Cross-laminated timber, face and edge fixing.
• Laminated veneer lumber in softwood.
• Timber to steel connections.
• Insertion at an angle to the grain.
• Compression and tension reinforcement perpendicular to the grain.

• CLT rules carried in the assessment. Screws in CLT have an outer thread diameter of at least 6 mm and an inner thread diameter greater than the widest gap in a CLT layer. Panel thickness and edge surface penetration are each at least 10 times the diameter, and the edge surface spacings do not vary with the angle between screw axis and grain.
• Spacing buys member thickness. Where spacings parallel to the grain and the end distance reach 25 times the diameter, the minimum member thickness drops to 30 mm up to 8 mm diameter, 40 mm at 10 mm and 100 mm at 12 mm and above, and the unloaded edge distance may be reduced to 3 times the diameter.
• LVL is designed on the veneer plane. Screws in laminated veneer lumber are arranged only perpendicular to the plane of the veneers, and the withdrawal parameter is applied with the characteristic density of the LVL capped at 500 kg/m³.
• Reinforcement in two modes, at defined angles. Carbon steel BM FT Quick Drill screws carry compression reinforcement perpendicular to the grain at 45 to 90 degrees, and fully threaded screws carry tension reinforcement at 90 degrees. A screw acting as reinforcement is exempt from the 50 per cent single-screw reduction that applies to other wood-to-wood connections.
• Head-side thread as an alternative to pull-through. For full-thread and double-thread screws with a countersunk or wafer head, the thread withdrawal in the head-side member may be taken as an alternative to head pull-through. For cylinder heads the head part is not considered.

All Bi-Mirth screws are available in:

• the Screw module;
• the connection detail calculators: panel-to-panel (half-lap, spline and butt joint), slab-to-wall, wall-to-wall, floor-to-wall;
• the rib-deck calculator, for flexible connection design to Eurocode 5.

The screw families marked for reinforcement additionally appear in the reinforcement connection details: beam notch, beam penetration, and beam compression perpendicular to grain.

Design follows EN 1995-1-1, with axially loaded screws verified to §8.7.2. Two clause behaviours come from the assessment rather than the code defaults: under §8.7.1 the effective diameter is the outer thread diameter, in place of the default of 1.1 times the thread root diameter, and clause 8.7.2(1)P lists buckling under compression among the failure modes, which the assessment quantifies for the carbon steel full-thread screws through an ideal elastic buckling load on an elastic foundation.