So you picked a self-tapping screw off a job site and it was just what you have been looking for but it didn’t come in a box that was labeled – it was just sitting there on the floor. What do you do? How can you ask for something when you’re not really sure what to ask for? The nice thing is that it isn’t so difficult if you know what dimensions to measure when you are asking your fastener sales representative to help you.
First describe the head. Is it a…?
There are other style heads available but these are the most common head styles that you should know. Once you can identify the head style that you are looking for, it makes things much easier.
To identify the shank size of the screw, it’s much easier if your screw is a hex head. When considering the shank size, think dress size. The smaller the number, the thinner the shank. The bigger the number, the thicker the shank.
The standard for the industry is:
• 1/4″ Hex Head = #6 or #7 or #8 shank size
• 5/16″ Hex Head = #10 or #12 shank size
• 3/8″ Hex Head = #14 shank size
Of course there always have to be exceptions just to keep things interesting.
In our case, we have needlepoint screws (aka zip screws) developed especially for the gutter industry with have high profile 1/4″ hex head but #10 washers and #10 body shanks. In the 70’s and 80’s, standard #8 screws worked fine for the gutter industry but when the quality of the wood used for homes changed, it was necessary to increase the thickness of the shanks so that the screws wouldn’t snap when hitting knots in the wood. We also added a filet underneath the head to give the screw a little extra strength.
Next, there is TPI or threads per inch to consider. As a rule of thumb, the less threads per inch, the screw is intended to be used in wood. The more TPI, the screw is meant for metal or metal studs. These are sometimes called out as ‘coarse threaded’ or ‘fine threaded’ screws. If you try and use a coarse threaded screw in metal studs or hard woods, the quality of the screw can’t really be blamed when it snaps although that happens all the time. It is simply misapplication and the more you know what screws were made for what applications, the less problems you will have when using your screws.
Now we get to the points of the screws.
Does the point look like a pencil point?
Does the point look like a drill bit tip?
There are other type points like Type 17’s used with woods and others but the two listed above are the most common.
And lastly, you should remember to state the plating that you need. Zinc plating is most common with under normal situations will last you about two years on average. Hot dipped galvanized is generally five years. But these are old school type plating. We have started stocking Dacronized®, ceramic type plating, which we normally have stocked in 500, 1000 and 1200 hour salt spray tested. They give you extra protection and even are available with the heads painted as well to match exterior applications.
When you are looking at a label on a box, the screws will generally be labeled something like “8-18×1 HWH SDS Z/P”. This would translate to #8
shank, 18 TPI by 1 inch long, hex washer head, self drilling screw (tek type point) zinc plated.
This is not everything that there is to know about self-tapping screws, zip screws and tek screws included, but it will give you a good baseline to start!