ISO double-threaded bolt

The double-threaded bolt looks like a metal stud with two types of thread: at one end a coarse wood thread, which screws into the beam of the roof, and at the other end an ordinary nut thread. It is the solution used when the covering cannot be lifted, but must be pierced, as happens with corrugated sheet or fibre-cement boards. After tightening, the adapter that supports the rail is fitted on the threaded end.

The usual sizes are M10, in lengths of 180, 200 or 250 mm, and M12, in lengths of 200, 250 or 300 mm; the length is chosen according to the thickness of the covering, the insulation layer and how deep it must penetrate into the timber. The hole is sealed with an EPDM rubber washer crushed on the covering, doubled by a metal washer and, sometimes, by butyl tape, and if this step is carried out correctly, the penetration presents no risk of leakage. The material is A2 stainless steel, so the fixings last without rusting over the service life of the installation. The bolts are always driven into the crest of the corrugation, not into the valley, where the water runs.

Double-threaded bolt (hanger bolt / stockschraube) of A2 stainless steel, with a wood thread at one end and a metric thread at the other, in usual sizes M10 (180 / 200 / 250 mm) and M12 (200 / 250 / 300 mm). Substrate: timber roof frame, with fixing into the rafter or into the boarding and sealing through an EPDM washer fitted together with a metal washer. The load-bearing capacity of the joint is given by the screwing depth in the timber and by the strength class of the timber and is verified by structural calculation for pull-out and shear, for the wind and snow loads at the site.

Who it suits

Suitable for outbuildings, stables and halls with a covering of corrugated fibre-cement or corrugated sheet laid on a timber roof frame, where fixing is done through the roof.

Terms explained

• Metric thread (M10, M12): The standard bolt thread, where the number indicates the diameter in millimetres.
• Pull-out: The force with which the wind pulls the bolt upwards, trying to take it out of the timber; the required screwing depth depends on it.
• Butyl tape: A sticky and elastic tape, applied additionally under the fixing part, so that water does not reach the hole.

Technical specifications

Recommended applications

• Fixing the PV structure on roofs of corrugated fibre-cement
• Roofs of corrugated or trapezoidal sheet on a timber roof frame
• Installation with a rail adapter screwed onto the metric thread
• Agricultural buildings and outbuildings with a covering on a timber support

Technical details

Generic product — standard specifications

The double-threaded bolt, also known as a hanger bolt or stockschraube, is the anchoring element used when the photovoltaic structure is fixed directly into the timber rafter or boarding, through the covering. One end has a wood-screw type thread, which screws into the rafter, and the other end has a metric thread on which the nut, the washers and the rail adapter are fitted.

The usual sizes on the market are M10 and M12, with total lengths between 180 and 300 mm, chosen according to the thickness of the covering, of the insulation layer and of the screwing depth required in the timber. The standard material is A2 stainless steel, for corrosion resistance over the service life of the installation, and the sealing of the penetration is achieved with an EPDM sealing washer compressed on the surface of the covering, sometimes doubled by a metal washer and by butyl tape.

The solution is used mainly on roofs of corrugated fibre-cement, corrugated or trapezoidal sheet mounted on a timber roof frame, where fixing is done in the crest of the corrugation. The load-bearing capacity of the joint is given by the screwing depth in the timber and by the strength class of the timber, and must be verified by structural calculation for pull-out and shear for the wind and snow loads at the site.