Pallet builds implies a lot of assemblies and one of the easiest and popular methods is screwing. But, the main question is: What types of screws I should use? What sizes of screws? The answer is: it all depends on your use. Nevertheless, like in every domain, some general rules prevail. The use of wood screws or chipboard screws works well.
The 1.5 rule
Whether you screw pallet wood or new wood, the general rule is "strength". The screw must be at least one and a half times the size of the piece of wood it is to fasten. For example, a euro pallet board is usually 22mm thick. The screw must, therefore, be at least 22mm x 1.5 (33mm). This means that we will usually work with 35mm screws. Working with 40 mm is quite possible but if we mill the wood in addition to predrilling it, we can quickly make the screw of the two boards protrude. Regarding the thickness of the screw, we can rely on 3.5 / 4 for a versatile use. If we take thicker screws, we are more likely to crack the wood and the extra strength of the screw is not useful in most cases.
Unless working with self-drilling or self-drilling screws, it will be necessary to predrill to avoid splitting the pallet wood. And personally, even with self-drilling, I predrill the wood if I have to screw near the edge.
For indoor or outdoor?
Are you building a pallet TV cabinet or an outdoor pallet armchair?
As far as everything inside is concerned, Bichromate screws do the trick (These are the most common screws in store, they are usually yellow / gold colors). It withstands slight humidity but not direct contact with water.
As for the outside, you absolutely need a stainless steel screw, otherwise your screws will rust in a few months and rust may leave a halo on the wood around the screw. Why not use stainless steel screws for everything then? The answer is simple: price.
The different sizes of pallet boards
The 1.5 rule still works here, just measure the thickness of the boards and do the calculation to get the necessary size. I was talking about a thickness of 3.5 / 4 mm for the screws. The only time I use thicker screws is when creating rafter-based structures, especially for workbenches. I know they're going to have to carry heavy loads, and they're going to take blows, so I usually leave on screws 5/6mm thick by 80mm long.
Wood screws brands and types
As far as brands and types of heads are concerned, it is more up to people's appreciation. I am used to working with Torx type heads but PZ heads also work very well.
However, I do not recommend the purchase of "low-end" screws for regular work. Low-end screws tend to have a head that gets damaged much faster (just force it a bit and it gets damaged) and when buying a 1000 / 2000 package, it is not uncommon to find defective ones in the package (not totally straight, head design messed up etc).
Things to remember
- The screw must be at least 1.5 times the thickness of the wood you want to fasten.
- Bichromate for interior uses.
- Stainless steel for exterior uses.
- On average a thickness of 4mm.
And to finish a little picture to illustrate all the different kinds of wood screws available on the market.
Ever tried to remove a broken or stripped screw, even if you bought the best one available? You can see this article to learn 4 methods to remove a broken screw!