the scrooz blog

Our decking screws are now available in our new branded trade and bulk boxes comprising either 500 or 1000 stainless steel square drive decking screws in either 304 or 316 grade standard head or trim head sizes along with a galvanised deck screw range for customers looking for an alternative to stainless steel.

We’ve just released the first of our decking screws installers kit comprising everything you need to for screw fastening your deck in one cost effective convenient pack, all inclusions are high quality branded professional deck fixing products and offer a substantial cost saving over buying separately

Our 10G kit includes :

• 1 x Smartbit auto countersink with replacement bits.
• 1 x Irwin adjustable countersink for angle drilling, board ends and obstructive areas where a Smartbit won’t fit.
• 1 x 3.5mm HSS ground drill bit for freehand pilot hole drilling.
• 1 x 5mm HSS ground drill bit for freehand clearance hole drilling in deckboards preventing jacking/splitting etc.
• 2 x No2 25mm square drive torsion impact drive bits.
• 2 x No2 50mm square drive torsion impact drive bits.
• 1 x No2 100mm square drive impact drive bits for restricted access areas.
• 1 x No2 150mm square drive impact drive bits for restricted access areas.
• 2 x 5mm 32mm long hex impact drive bits for batten screws.
• 1 x Bordo Quick Release driver.

Click the links to see more of our range Decking Screws and Deck Screw Fixing Kits

Torx and Square drive are both very popular driver bits although not as common as Phillips and Pozidrive. It’s widely known that Torx and square drive provide a more positive connection between fastener and driver and so less slippage and skipping out occurs, particularly when fastening into tough materials.

So which is best, well the amount of tightening torque you can apply to an item is all really about friction and mating surfaces. The bigger the mating surface the better the connection, if you laid out a Torx star drive shape in a single line you’d see it would be longer than a similar square drive so the answer is Torx, and interestingly this is the main reason for it’s production not as a security drive as most people think.

See our full range of screwdriver bits here

To get a nut and bolt assembly to operate at full strength all the threads inside the nut should be filled, during production of bolts and external threaded fasteners the first 1 or 2 threads are deemed sacrificial as they usually not fully formed during manufacture.

So it is generally considered that 2-3 full thread pitches should be considered the minimum amount to protrude through the nut once it is tight and this is likely to produce a full set of mating fully formed threads inside the joint. If however, the bolt is to be tapped through any material (timber/steel) then a further allowance should be made for possible damage to more threads as it is inserted.

So does it matter if I tighten the bolt head or the nut, good question.

As long as the assembly is the same style and size i.e. the head of the bolt and the nut take the same size spanner then the answer is no, whichever you tighten you’ll still be providing the same amount of torque on the whole assembly so the clamping action will be equal.

If the assembly is different, let’s say a bolt with a flanged head using a standard unflanged nut then it’s possible that you could overtighten the nut if only using this to torque up the assembly. The reason is that on some specific joints a tightening torque figure will be given, a percentage of the load that the designer wants is lost due to friction of the mating surfaces. So let’s say the recommended torque for the flanged bolt is 40N/mm this figure will assume a loss of say 10N/mm for the flange therefore the designer originally wanted 30N/mm. If you go ahead and apply 40N/mm to the wrong end (nut) then you can see you have overloaded it.

So although it is fairly rare there are some instances where it does actually matter.

More about Bolts here

This is a popular question, so how do you know how long the thread is on a bolt, well manufacturers generally use the same standard so ISO Metric bolts in mild or high tensile steels all use this formula

For total lengths up to 125mm the thread length is 2 x diameter plus 6mm

For total lengths from 125mm to 200mm the thread length is 2 x diameter plus 12mm

For total lengths over 200mm the thread length is 2 x diameter plus 25mm

Total lengths are all taken from under the head and all diameters are thread diameters not heads.

This rule applies to hexagon head bolts only, generally other types of fasteners such as carriage bolts will have longer threads (due to the application) and this length is determined at the manufacturers discretion. Fully threaded hexagon bolts are also available and are commonly known as setscrews.

For more information about our Bolts click here

All hexagon bolts have markings on the head to tell you what type of bolt they are and give you the  tensile strength. Metric bolts will have 2 numbers separated by a dot, these numbers are the code for the tensile strength with the number left of the dot being the ultimate tensile strength (max stress before breakage) and the one on the right is the yield strength (max load before permanently deforming). The most common type of High Tensile bolt is 8.8grade but there are several others such as 9.8, 10.9 and 12.9 etc.

Imperial bolts use a radial line marking system on the head along with a single number ranging from 0-8 to denote the strength. Typically a bolt with 3 lines pointing towards the middle of the head with a number 5 and above will be the most commonly found.

You may also see other marking on the head of the bolt, perhaps some letters or a logo, these are the head markings of the manufacturer and are optional, it just allows the manufacturer to recognise or trace their bolts if required.

Here’s a link to our standard hex bolt range

Although we often use the term Type 17 Screw it doesn’t really refer to the fastener as a whole, the type 17 reference is a manufacturer’s term for the point shape on the end of the screw. When screws are being made the design will include many features, head style, drive type, shank style, material, plate finish etc. and of course the point type. Examples include type 23, type A, type AB, gimlet and type 17.

So just to clarify, type 17 is actually the point end and for type 17 this is a sharp pointed design with a cut out flute to help capture and remove the waste allowing a self drilling type function similar to a drill bit. This self drilling action prevents wood fibres separating which leads to splitting and so these screws are very useful for close to edge work, they  also benefit from fast insertion and self centering starts and so are ideal for use with powerdrivers.

The sharp point means you can also use them in thin steel sheeting without pre-drilling e.g. fixing roofing and cladding sheets. At Scrooz our type 17 fasteners are all branded under our Razr range which denotes their self drilling thread cutting function along with other features.

See our full range of Type 17 Screws here

Drywall or plasterboard is generally made up of a paper liner wrapped around a gypsum plaster inner core and is fixed to wall frameworks using nails, adhesives and of course screws.

Drywall screws are specifically designed for this application and have the following features :

Bugle head countersink which designed to hold the board tight without breaking through the paper liner which is what happens when a standard wood type screw with an angular countersink does.

The pitch of the screw can be classified as either coarse or fine. The more coarsely threaded the screw, the tighter it holds. Plus, since it contains fewer threads, it screws into place faster. On the other hand, although finely threaded screws take longer to insert, they have sharper points, making it easier to insert the screw in the first place. You’re meant to use coarsely threaded drywall screws when you’re attaching the drywall to softwood studs, while finely threaded drywall screws are meant to be used when you’re attaching the drywall to light metal studs.

They are always plated in either a black oxide finish or a zinc plate for corrosion protection as it’s likely they will be covered over with a wet skim of plaster to finish off the joints, driver types are mostly Phillips No2. They are also available in a self drilling form for fixing to heavier steel sections and in collated ribbons for use with auto feed systems.

See our full range of drywall and plasterboard screws here

The preferred fastener for this application seems to be the wing drill screw however the fact is we don’t recommend any direct screw fixing to steel joists.

Differential movement is just as it sound’s, it’s the amount of movement likely to occur between different objects. With a timber deck on timber joists it’s fairly probable that growth and shrinkage will be about the same, certainly in hot climatic conditions this movement can be quite considerable, however the total amount does vary dramatically dependant on timber species, moisture content, location, size etc etc.

The issue with screw fixing decks to steel joists is the higher degree of movement in the timber compared to a much lesser steel expansion leads to excessive forces being created in the fasteners which can result in a scissor type shearing action and obvious failure. This doesn’t happen in all cases and some manufacturers agree that wing drill screws can be used on covered decks however we take the view that the timber should not be screw fixed to the steel at all.

The best fixing method is to bolt a timber batten to the steel joist (on top or on the side) and then use a standard deck screw to fix the board into the batten, the bolts will be thick and strong enough to resist this potential shearing action and the screw fixings will move at the same rate as both timbers.

Some manufacturers also recommend hardened steel nails for deck fixing to steel and whilst we agree the nails would allow more flexibility than screws during movement we have not yet seen any long term test results to see if the joint loosens and therefore couldn’t advise on this.