To identify whether the thread is tapered or parallel, look at the diameter of your thread. If the thread diameter gets thinner towards the end, you are looking at a tapered thread. On the contrary, if the thread diameter is the same at the top and the bottom of the thread, you have the parallel thread.
There are three standard thread series in the Unified screw thread system that are highly important for fasteners: UNC (coarse), UNF (fine), and 8-UN (8 thread).
NPT/NPS threads have a 60° angle and have flattened peaks and valleys (Sellers thread form) where as BSP threads have a 55° angle and have rounded peaks and valleys (Whitworth thread form).
Metric thread pitch measurements are read differently than standard ones. While for standard thread pitch measurements the lower number is coarse thread and the higher number refers to fine thread, in metric this is opposite. M10-1.50 is a coarse thread denotation while M10-1.25 is a fine pitch.
General Instructions. Measure screw diameter, or screw size, by measuring the width of the threaded part of the screw. This corresponds to the first number of the thread size. For inches, any diameter smaller than 1/4" is indicated by a number, referenced in the table below (e.g. 8 corresponds to 0.164").
There are Standard threads, ACME threads, Buttress threads, and Square threads. Each of these threads may be used in clamps and vises for different reasons.
Metric threads are designated with a capital M plus an indication to their nominal outer diameter and their pitch: This bolt is M10 x 1.5 - which means the outside diameter is 10mm and the threads are 1.5mm apart (the most common thread pitch for M10).
Metric threads are measured by their pitch. That is the distance from the crest of one thread to the crest of the next measured in millimetres. The pitch of a metric thread can be checked by direct measurement with a metric rule. Imperial threads have their pitch measured indirectly as a given number of teeth per inch.
Although BSP is a foreign thread, it isn't actually metric. This is why it comes in Imperial sizes: 1/8, 1/4, 1/2, 3/4, and so on. Use a calipers to measure the outside diameter (OD) of the threads.
NPT thread is angled at 60 degrees while BSPT is angled at 55 degrees. This means you can actually get a BSPT male fitting to tighten down to an NPT female.
For example a 1/2 inch BSP thread (see above) actually measures more like 3/4 inch with a ruler. The size was originally based on the inside diameter, measured in inches, of a steel pipe for which the thread was intended.
You can identify any BSPP or BSPT fitting accurately by measuring across the thread from one side to the other. BSPP fittings can be measured more simply, and their specifications can be identified with a few basic calculations. To determine the thread size: Measure the thread's outer diameter (OD) in inches.
Metric thread is the most widely used today, and can otherwise be referred to as 'ISO Metric' or 'M'. Both coarse and fine thread fasteners are available, and can be supplied in a wide range of materials and sizes – with a number of popular DIN standards.
There are two common forms of threads: straight threads and tapered threads. Straight threads have a parallel profile that remains the same diameter throughout the part. Tapered threads taper along with the thread profile and become smaller in diameter as the part moves down.
Classes 2A-2B
Class 2A external threads have an allowance, Class 2B internal threads do not. Classes 2A and 2B, for most engineering applications, offer the optimum thread fit that balances fastener performance, manufacturing convenience and economy.
Typically, SAE sockets and wrenches are used on American-made cars, as mentioned previously, however, when it comes to working on imported cars (assuming you're in the USA) you'll most likely be looking for metric units of measurement.
Metric and SAE fasteners are measured differently and with different vocabulary. SAE nuts, bolts and screws are measured by their thread count, or TPI (threads per inch) and their length. Metric fasteners are measured by length and pitch, or the distance between threads.
Designation. A metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D (the maximum thread diameter) and the pitch P, both expressed in millimetres and separated by the multiplication sign, × (e.g. M8×1.25).
The first number is the nominal diameter. 10mm is larger than 8mm. The second number is the thread pitch. The nut and the bolt need the same pitch.
So an M8 bolt would have a shaft diameter that's slightly under 8mm which means that the bolt should fit through an 8mm hole.
For producing recessed holes for cap screw heads. Excellent for drilling Steels (Magnetic soft steel, Structural steel, Carbon Steel & Alloy Steel) and Synthetic materials.