The UNF 2A thread chart provide the dimensions for fine threads. The UNF 2A thread chart will help you to understand the differences between fine threads and coarse thread. Use fine threads whenever you need high strength from your screw or bolt, or when the screw have to be inserted into tight space.
Use coarse threads whenever you are trying to speed up the process of assembling your part, or if the parts to be assembled may be dirty. Fine threads have more ridges then coarse threads of the same length. Additionally, fine threads leave more metal in the core of the bolt.
How to Use the UNF 2A Thread Chart
This increase the tensile strength of the bolt, which means that a bolt with fine threads can take more load before it begins to shear than a bolt with coarse threads of the same diameter. Fine threads are also used whenever the material to be fastened is thin. Coarse threads require a certain thickness of material to engage with the part to be fastened, but fine threads will engage better with thin-walled material due to the increased number of ridges on the fine threads.
Designers will typically use UNF threads whenever the weight or the available space for the part are limited. The UNF 2A thread chart will show the size of the drill bit that the machinist will use to tap the hole in the part. Thus, the UNF 2A thread chart can help you to plan the size of the hole before you begin to machine the part.
Another reason to use fine threads is for vibration resistance. The angle of the flank of fine threads are shallower than that of coarse threads. This means that bolts with fine threads will have to rotate further before they will loosen.
This feature of fine threads can be helpful in machines where the bolts is subjected to vibration, as it will allow bolts with fine threads to maintain their preload. However, fine threads are not a replacement for locking feature on bolts, although they will reduce the rate at which the preload of bolts with fine threads will drop in assemblies. Bolts come in many different tolerance class.
The most common class for commercial applications is class 2a. Class 2a is used as the standard for bolts and screws because it allow for easy assembly of the parts, while maintaining the strength of the threads. The UNF 2A thread chart shows the dimension for class 2a bolts. Thus, you can use this thread chart to ensure that your bolts threads is within spec.
For parts that will be assembled many times, it is recommended that go and no-go ring gauge are used to inspect the threads. Inspecting the threads during assembly will save time and money down the road in cases of finding bolts with bad threads after they have been plated. Fine threads are used in different situations than coarse threads.
Fine threads are used if you need additional strength in your bolts, if the materials to be fastened has thin walls, or if the bolts will be subjected to vibration. Coarse threads are used if you need to speed up the assembling process of your design. The UNF 2A thread chart makes it easy to compare the stress area and the size of the tap drill for each thread size.
Thus, the UNF 2A thread chart remove the guesswork involved in choosing between fine and coarse threads. Many shops will have both fine and coarse threads in there inventory, as there are various applications for both types of threads. However, it is important to not force a fine thread into a coarse thread hole.
This will damage both the bolt and the hole. To avoid forcing fine and coarse threads into each other, measure the diameter of the hole with a caliper, and use a pitch gauge to measure the thread count. Using both tools will ensure that the screw that you are purchasing is the correct type for the hole in the part.
The relationship between the size of the threads and the size of the drill bit that will be used to tap the hole in the part to recieve the screw is consistent and easily seen on the UNF 2A thread chart. This thread chart is extremely useful when you are programming your CNC machine, or when instructing another machine operator on the steps to machine the part. This thread chart will allow you to make your decision, and to have documentation to back up your decision.
