To measure screw length, use a ruler to measure from the point where the screw head would sit flush with a surface to the tip, which varies by head type. For countersunk screws (flat on top), measure from the flat top of the head to the tip. For most other screws (like pan head or round head), measure from the bottom of the head to the tip.
How to Measure Specific Screw Types
- Countersunk (Flat) Head Screws: Place the ruler on the flat top of the head and measure to the tip.
- Pan Head, Round Head, and Hex Head Screws: Measure from the flat bottom surface of the head to the tip of the screw.
- Raised Countersunk Screws: Measure from the flat portion of the head where it meets the material surface to the tip.
- Grub Screws (Set Screws): Measure the entire length from one tip to the other, as these have no head that protrudes.
Tips for Accuracy
- Use a Ruler or Measuring Tape: A simple ruler or measuring tape will work for most screws.
- Vernier Caliper (for Precision): For high precision, use a Vernier caliper, which offers two flat points of contact for greater accuracy.
- Understand the "Usable" Length: The goal is to measure the portion of the screw that goes into the material or the depth of the hole it will fasten.
