Phillips screw symbol and screwdriver tip with conical flanks. The Phillips Screw Company and the American Screw Company patented a cross-head screw with parallel flanks which prevents the ejection force during tightening or loosening.

1. a. A cylindrical rod incised with one or more helical or advancing spiral threads, as a lead screw or worm screw. b. The tapped collar or socket that receives this rod.

Phillips Head Screwdriver

A flat head screw is used when a higher amount of torque is needed. It’s shape allows it to be tightened tighter without the tool slipping. A philips head screw is used to prevent overtightening by allowing the tool to slip when a certain tention is reached.

What this means is that a screw considered to be 8 mm long may actually measure 7.6mm or 8.0mm. It may be measured from under the head or the overall length. The actual diameter of an M3 screw is usually about 2.9mm, an M2. 5 screw is 2.4mm and an M2 is 1.9mm. We give both the overall length and the thread length.

How to Measure the Size of a Bolt

1. Step 1: Measure the shank’s diameter. The shaft of the bolt is called the shank, and its diameter is the first dimension used to describe a bolt size.
2. Step 2: Determine the thread pitch.
3. Step 3: Measure the length of the shank.
4. Step 6: Measure the length of the threaded portion of the bolt.

Metric Imperial Screw Conversion Chart

Spanner (wrench) sizes

A gage number like “6” is the diameter and the length is the length of the screw that goes into the wood not inclusive of the head unless it’s a flat head. The smaller the gage number the smaller the screw diameter (opposite of nails and wire diameter).

#14 is close to, but not exactly the same as, 1/4-inch.) The major diameter in Unified threads = 0.060″ + 0.013″ x (numbered diameter). But the given diameter formula only is valid for the gauge numbered screws.