As an expert in mechanical specifications and fasteners, I can explain the term "3 8 16 UNC" which is commonly used in the context of threaded fasteners, such as bolts, screws, and nuts.

"3" refers to the number of threads per inch. In this case, it means there are 3 threads per inch of the fastener.

"8" is the diameter of the threaded fastener in 1/8ths of an inch. So, an "8" would indicate that the fastener has a diameter of 1/8 inch.

"16" is not a standard part of the UNC (Unified National Coarse) threading system. It could be a typo or a misunderstanding. The UNC system typically includes a number that corresponds to the number of threads per inch, not a separate number like "16". The number following the diameter in a UNC thread specification usually indicates the thread pitch, which is already represented by the "3" in this case.

"UNC" stands for Unified National Coarse, which is a threading standard used in the United States and Canada. It is a widely used system for defining the size and pitch of threads on bolts, screws, and other threaded fasteners.

To summarize, "3 8 16 UNC" seems to be a miscommunication or error because the "16" does not fit the standard UNC threading notation. The correct specification would likely be "3 8 UNC," which would mean a fastener with 3 threads per inch and a diameter of 1/8 inch.

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? -20 �C UNC -3B �CLH means this is a ? inch diameter thread with 20 thread per inch, manufactured in accordance with Unified National Coarse Standard. ... 7/8 �C 20 �C UNEF -2B stands for internal normal precision thread with a diameter of 7/8 inch and 20 threads per inch, which is Unified National Extra Fine Standard.read more >>