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Material

All DGS Friction Stays are made from high grade stainless steel; we must therefore strongly recommend that they are secured using stainless steel high grade stainless steel screws.

Austenitic/Carbon Steel Bi-metallic Screws

The head and majority thread portion of an austenitic bi-metallic screw is made from austenitic stainless steel. The last two or three threads and drill point are manufactured from carbon steel. The austenitic portion of the fastener gives the corrosion resistance you require, while the carbon steel gives you the hardness necessary to self drill into steel, effectively pulling the austenitic portion behind it. The austenitic head and thread can be distorted by misuse or incorrect choice of screwdriver bit. If the carbon steel tip remains in contact with the reinforcement, corrosion may occur. Worst still should the weld break, you are not fixed into reinforcing. That is why it is vital that your bi-metallic screw is manufactured and applied so as to leave the carbon steel portion sitting clear in the void of the reinforcement chamber.

Marutex Screws

Not to be confused with ordinary 410 martensitic stainless steel, Marutex is manufactured from modified martensitic material and contains higher amounts of chromium (13.5I), some nickel (0,48%) plus molybdenum (2%), which is not found in 410 martensitic. Molybdenum is generally used in higher grades of austenitic, such as 316 marine grade.

Marutex is heat-treated in such a way as not to destroy the chromium rich passivation layer, so it needs no sacrificial coatings to enhance its corrosion resistance. This process also gives it excellent hardness and ductility. Marutex can be self-drilled easily into steel and aluminium reinforcement without any distortion.

Declaration of Conformity to BS7412:2007

The standard BS7412:2007 covers the material requirements for fasteners used in the window and door industry.

The standard refers to the performance of fastenings to the BPF (British Plastics Federation) WG (Window Group) publication 363/1. Specifically 363/1 requires fasteners securing non-stainless steel hardware to have a corrosion resistance in excess of 240 hours in a neutral salt spray test (SST), tested in accordance to BS7479:1991. Fasteners securing stainless steel hardware must achieve in excess of 500 hours. Testing is to be carried out by an accredited independent UKAS laboratory.

With reference to stainless steel hardware, DGS (as well as the BFP) do not recommend the use of carbon steel screws in such applications as friction stays, because of the increased risk of corrosion due to an electrolytic reaction between two dissimilar metals and the potential exposure to aggressive environments such as coastal areas, which can accelerate the onset of corrosion. Window hardware attached using stainless steel fasteners supplied by DGS should help to ensure the long service life of the finished window or door.

All DGS Carbon Steel and Stainless Steel Screws conform to the guidelines set out in BPF WG3621/1 and in turn BS7412:2007. Independent test results are available on request.

We strongly recommend that if you are fixing stainless steel hardware, such as friction stays, you use either Marutex® or austenitic/carbon steel bi-metallic screws.

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Screw Head Types

Shallow Pan

• Ideal for securing friction stays
• Good clamping properties from the flat under-head
• Collar under the head gives positive screw location

Shallow Flange Head

• Ideal for securing friction stays
• 1mm increase in head diameter over shallow pan allows for even greater clamping properties
• Collar under the head gives positive screw location
• Greater security with bigger diameter screw and head