ACME Thread Plug Gage

WESTport Gage provides a complete line of standard and special General Purpose ACME GO/NO GO Thread Plug Gages in compliance with ASME B1.5 - 1997. Acme Thread Plug Gages are used to gage an internal threaded product.. The ACME thread list of diameters listed here and their associated pitches are recommended as preferred. They have been specifically selected to meet requirements with the least number of items. In doing so this keeps the inventory of gages and tooling to a minimum in an effort to reduce costs.
There are three classes of fit for ACME General Purpose thread gages; 2G, 3G and 4G. Centralizing ACME threads have classes of fit which are 2C, 3C and 4C. ACME threads feature a 29 degree angle of thread which is the angle between the sides of the thread measured in an axial plane. ACME Thread Plug Gage lengths and blank standards are compliant to ASME B47.1 Centralizing ACME thread gages, Multiple start ACME thread gages and any special requirements will be priced on request.

Definition and Uses

Screw threads fall into a few different categories: normal, square and ACME. These thread types different in shape, strength, and usage. You are probably familiar with normal screw threads like the ones below.

Fig. 1 Normal thread examples

Normal threads are used in thousands of different applications and products. You can tell from the image that the thread is triangular, thin, and sharp. Unlike normal threads, ACME and square threads are blunt and used in very specific ways.

ACME threads are trapezoidal, which means that they are not sharp like a normal thread, but the base of the thread is slightly wider than the top, unlike a square thread.

Fig. 2 ACME thread example

Fig. 3 Square thread example

ACME thread form is commonly used for applications that involve high accuracy or very large loads. They are often used for lead screws (which are screws that convert turning motion into linear motion) and in lathes and vises, but are also found in many other applications and products like jacks and aircraft flaps. The square thread form was originally used for these applications, but the trapezoidal or ACME form has mostly replaced it because it is easier to manufacture, and it is stronger than the square form.

Types of ACME Threads

ACME thread forms have a thread angle of 29°, and the similar trapezoidal metric thread form has a thread angle of 30°. Both are commonly used, but the ACME thread is the most prolific throughout the world, even in countries that use the metric system. ACME threads and gages come in two main types with the respective classes of fit.

• General purpose ACMEs are used in a wide variety of machines. They have a clearance on all diameters, which allows for free movement. General purpose ACMEs fall into three classes of fit: 2G, 3G and 4G. (Class of fit refers to the allowable range of tolerance, or amount of interference, where 2G has the loosest fit and 4G the tightest.) They are used in applications that do not require strictly holding major diameter.
• Centralizing ACMEs differ from the general purpose only in the clearance of the major diameter. Centralizing ACMEs have limited clearance at the major diameter, which keeps alignment and prevents wedging, binding, and crossing threads. Five classes of fit exist for centralizing ACMEs: 2C, 3C, 4C, 5C and 6C. Classes 2C, 3C and 4C are most common.

ACME Thread Gages

Because ACME threads are often used for precise manufacturing machines, it is vital to routinely inspect and calibrate the threads. An Acme thread ring gage is used to check tolerances; it will feature a GO and a NO GO member. If the threads are within tolerance, the GO member should completely screw on, and the NO GO member should not. WESTport Corporation offers ACME GO/NO GO thread ring gages for external threads in classes 2G, 3G, 4G, 2C, 3C, and 4C. These top-quality gages comply with ASME B1.5-1997. Acme thread set plug gages are used to insure that the thread ring gage is calibrated properly and are compliant to ASME B1.5-1997.