Free Click & Collect In 1 Hour From New Southgate Store | Free Delivery Over £500 inc VAT
Free Click & Collect In 1 Hour From New Southgate Store
Ex VAT
Inc VAT
  • Stores
Search
Trolley

Tools & Fixings Buying Guides

Screw Threads

Threads are the helical ridges that run around the external shank of the screw - however, they serve a greater purpose than just giving screws their iconic look! From driving power to installation time, this guide will explore the range of screw threads and how each one serves their own purpose.

Shop All Screws

Screw Thread

Intro

You may know that threads are what provide screws with their unmatched grip strength and keep your materials firmly together, locking the wood in place. However, what you may be less aware of is just how many different thread styles, shapes and types are available. This guide will take you through the most common screw threads and what applications they tackle best, as well as explore some lesser-known thread styles.

If you need help dissecting what different threads, heads and gauges do, take a look through our other Screw guide pages:

Screw Anatomy

Before we take a look at the different types of screws, it's a good idea to get acquainted with their different parts first:

screw anatomy

Screw Threads: Partially, Fully or Dual

All screws have ‘threads’, which are the helical shape that runs around the cylinder of the screw. However, not all screw threads are going to work with all applications; each one is specifically tailored to a different task or material. Factors such as whether the screw is partially, fully or even dual threaded can all impact the outcome of your fastening job:

threaded screws

threaded screws

1) Partially-threaded Screws

  • This external threading only runs partially down the shaft
  • Used for extreme holding force
  • Ideal for when precision and alignment is vital
  • These screws have less weak points that could lead to bending or cracking

2) Fully-threaded Screws

  • Fully-threaded Screws
  • This external threading runs all the way down the shaft
  • Used for where grip strength is critical
  • Can withstand greater forces than partially-threaded screws
  • Rarely shear and tend not to loosen as much

3) Dual-threaded Screws

  • Has a double start thread running along the body of the screw
  • They often have a larger pitch, or TPI (threads per pitch)
  • They can be inserted or removed twice as fast as a single-start thread
  • Able to hold material together more securely

Common Screw Threads

Some threads have sharp designs meant for drilling directly into softer materials, such as wood, however, others will require a pre-drilled hole, such as those going into masonry. By paying attention to these characteristics, you can ensure that your choice of screw is going to provide you with the most appropriate strength for the project at hand.

Below are some of the most common screw thread types:

Screw Thread Chart

Thread Name Key Features Common Attributes
Twin Thread
  • A pair of threads that runs along the screw body
  • Installation is twice as fast than with single-threaded screws
    		•
  • Hardwood, e.g. mahogany & oak
    		•  twin thread screw
    Coarse Thread
  • A screw can be classified as coarse if it has less than 16 threads per inch
  • Also referred to as ‘spaced threads’
    		•
  • Softer materials, e.g. hard/soft wood, plastic & plasterboard
    		•  coarse thread screw
    Fine Thread
  • A screw can be classified as fine if it has more than 16 threads per inch
  • Also referred to as ‘metric threads’
  • Medium steel applications, e.g. 5-12mm
    		•  fine thread screw
    Serrated Thread
  • These screws have small serrations all the way around the crest of the thread
  • Reduce the force needed to insert the screw due to their lower driving torque, speeding insertion time
  • Help penetrate materials without them splitting
    		•
  • Materials liable to splitting, e.g. plywood & oriented strand board
    		•  serratedthread screw
    Hi-Lo Thread
  • These screws include a double-lead thread in which the Hi thread possesses greeted sharpness than a conventional thread
    		•
  • Materials with a low density, e.g. softwood, plastics & thin sheets
    		•  hilo thread screw

    If you’d like to understand more about screw threads, including information on thread protection or formulas to determine a thread’s strength, check out this helpful PDF Document from the Fastenal Engineering & Design Society.

    Parallel VS Tapered Threads

    There are two main profiles that appear on fasteners in terms of their threads: parallel and tapered. The thread titles may seem self-explanatory, and thankfully when dealing with screws this aspect is already decided in the screw type, but it's still important to note for pre-drilling purposes (parallel threads may need more pre-drilling than tampered ones)

    PARALLEL THREADS

    parallel thread screw

    Parallel threaded fasteners will have a consistent diameter all the way down the part, giving it a parallel profile. Almost all bolts have this kind of thread, and some screws such as those with a B-point or self-drilling screws.
    TAPERED THREADS

    tapered thread screw

    Unlike their parallel counterparts, a tapered thread profile will decrease in diameter as you travel down the part. Most screws have tapered threads, giving them their iconic pointed shape.