Go plug-less and ‘hi-lo’

Faster and easier installation of windows and doors means ditching fiddly plastic plugs and understanding why a hi-lo thread holds the key to success. Andy Holland, technical andmarketing manager at Rapierstar, explains why.

Why should the design and quality of a frame fixing make any difference to how easy they are to use and the quality of the finished installation? Like most things, not all frame fixings are the same, which means your choice of fasteners for a window or door installation will have a big impact on how well the finished product will look, function and perform long-term.

Choose well and you’ll save a lot of time and hassle, as well as attracting the highest customer satisfaction ratings.

There are two main methods are available: fixings with plugs, and those that are plug-less. Both are suitable for timber and PVCU frames, with best practice being to position fixings at 600mm centres, with corner fixings being between 150mm and 250mm from external corners, and a minimum of 150mm from the centre line of a transom/mullion.

We think the plug-free route is best for a number of reasons. With our StarFix fasteners, all that’s required is a 6mm or 6.5mm pilot hole through the frame reinforcement and brickwork, and the screw can be driven into place with ease; there is no need to drill to accommodate a plug or anchor, and plastic waste is also reduced.

Not all plug-free fixings are the same, however. When the screw is driven into the masonry, dust and debris is produced. This has to go somewhere but it has nowhere to go if the thread height is the same down the length of the screw. This build-up can lead to reduced grip as the thread may end up simply cutting into dust as the screw is driven deeper into the masonry, resulting in poor pull-out strength.

The solution comes with a ‘hi-lo’ thread form. Here the thread height varies to fulfil different roles: the higher level thread cuts into the masonry, and the alternate low thread allows for dust to be compacted. This is the principle that provides ultimate grip and allows for multiple re-fixing without stripping the tapped hole.

The hi-lo thread form will also help prevent unreinforced PVCU frames jacking or twisting as the frame fixing is driven through. Some fastener threads may grip too much, and this can easily cause distortion of the profile if it lacks lateral rigidity in the absence of reinforcement. That’s why the thread design along the length of the fastener must be optimised to cater for the contradictory requirements for the different material types: plastic, brick, metal, etc.

The head design must be well-designed and manufactured to a consistently high standard to ensure optimum drive efficiency with every fixing to allow for improved grip. The precision Stardrive ST30 recess reflects this thinking, which is why it features across the StarFix range. This also helps to extend bit life for another cost-saving benefit.

Despite the tiny cost of fasteners as part of the whole window or door, they make a huge difference on the quality of the finished installed product and the speed and ease of installation. Seeking specialist advice will help you arrive at the best result, which Rapierstar offers through a wide range of downloadable technical resources.

The Recommended Fixing Manuals (RFMs), which Rapierstar produces for all the major profile systems, are easytouse and show which fasteners are best for manufacturing, as well as when coupling assemblies and installing bay windows.

And even if you face a situation that isn’t covered by an RFM, there are more than 120 fastener types available from Rapierstar alone, one of which could be the ideal solution for whatever fixing challenge you are facing.