The importance of a correct size and depth pilot is often underestimated, and is critical to maintaining the integrity of a fastener when installing. Preparation and proper pilot hole size is the key to success.
We recommend a pilot hole be used for all our fasteners.
Our tapered cut thread woodscrews require either a tapered or two stage pilot hole. Single width pilot hole is not suitable, because the screw is largest under the head, so a hole drilled at the shank or gauge diameter, will be too large for the the threaded portion of the screw to find purchase, and a small minor diameter hole is too small for the plain shank, which increases the risk torsion failure of the screw where the head will break off.
Its important to remember, than even our high tensile brass screws are still a relatively soft material, and the silicon bronze is the equivalent strength of mild steel.
Timber and testing:
It is important to test your pilot hole size on the timber. While our table gives you the measurements of the screws, different timber characteristics - grain; density; moisture; strength vary.
How do you know your pilot hole is the right size?
Modern battery drills with excellent torque and speed control are ideal for driving slot, square and torx drive woodscrews, as long as your pilot hole is of sufficient size as to allow the screw to be driven without excessive torsion load.
To small diameter or too shallow in depth:
- Screw becomes difficult to drive when 1/2-2/3 into the timber
- driver jumps out of head/strips out
- drill pitch changes
- drill may stop
- screw snaps
If you have any of these things happen - back the screw out - feel the temperature the screw - warm is normal, if its too hot to touch, you are overloading the fasteners and failure is imminent if you continue.
Drill the pilot hole out 0.5-1mm, confirm depth of both pilot holes - test with a new screw. Repeat if needed.
To big (you cant have the hole too deep!)
- Screw drives very easily - there should be some torsion load
- excessive movement once in timber - if the screw is moving side to side and is not snug in the timber
- head keeps spinning once driven into timber and does pull tight
How to drill a pilot hole
Two step method:
Firstly - you need to know what size to drill the two holes - we have included a table below to help you with this, but that is just a guide, and particularly with your minor diameter, can vary half to one drill size depending on the screw length, so its important to measure your screws before you start.
- Shank/Major hole size - this should be no more than 0.5mm smaller than the fastener itself - our table guide has these listed.
- Major hole depth - this will vary depending on your screw length - the hole should be at least as deep as the plain shank length (approximately 1/3 overall screw length)
These holes can be drilled with a standard/short drill for a majority of screws, and for countersunk screws, you can get these drills with a countersinking attachment as well, some have stoppers as part of the design so that you get the right size countersink for the screw gauge every time.
- Minor hole size - this is measure on the shank of the screw between the threads close to the tip (see image below). Its important check this measurement on the fasteners you ordered, due to variation in different lengths from the table provided.
For most fasteners over 1 1/2" in length, it is likely you will need a long series drill bit for the hole to be deep enough.
- Minor Hole depth - It is critical that this hole depth be at least the length of the screw, the risk of fastener failure increasing significantly if the tip encounters solid timber when being installed, especially on longer screws in hard timbers.
Three stage hole:
You'll notice on our chart that the 24g screw has two pilot hole sizes - on longer fasteners you may need to add an additional intermediate size and depth hole to create the correct 'taper' in the straight holes for the fastener.
There isn't a right or wrong order in which to drill your two stage hole, doing the shank hole first is generally easier.
Single Tapered hole:
As the title suggests - this method uses a special tapered drill bit to make a suitable size hole for the screw gauge in a single go, and do come with a countersink as well.
With a tapered countersink drill, you simply drill the hole to the appropriate depth for your fastener.
If you are drilling a lot of holes the same size for example when doing a deck, getting the right size tapered countersink drill will make your pilot drilling a lot faster
