From the book, M14 Rifle History and Development:

"M2 Type Bipods

The M2 bipod design was standardized in December, 1959 and improvements were added later. M2 bipods have been produced in the United States, Taiwan and China. Chinese copies of the M2 bipod do not have as excellent a reputation as compared to the USGI and Taiwanese models.

Taiwan models - The Taiwanese M2 bipod is reliable and suitable for civilian use. Beginning around 1998, some Taiwanese M2 bipods were sold to the U. S. Navy through Sarco, Inc. (CAGE Code 8R320). Taiwanese M2 bipods are made by Wayne Machine Inc. of Taipei, Taiwan. Taiwanese copies of the M2 bipod may have W M I stamped on the yoke. Taiwanese bipods sold by Sarco to the U. S. Navy do not have the W M I mark.

Early Taiwanese bipods were brazed but failed routinely. Otherwise, Taiwanese bipods are welded and have had no problems through thousands of rounds of automatic fire. Some of the Taiwanese M2 bipods were installed on M14 rifles and used in combat in Afghanistan in 2005. Seven of these bipods were removed from combat service in July, 2005 because each suffered the loss of the retaining pin holding the spring and button in one of the leg folding pushbutton assemblies.

Chinese models - The Chinese M2 bipod is marketed by Norinco. The Chinese versions will have the W M I marking. If the yoke screw requires a hex head wrench to tighten or loosen, it is a Chinese bipod.

USGI models - An American made USGI contract M2 bipod will have the following markings on the yoke: U. S. 7790833 BIPOD RIFLE M2 or U. S. 7790688 BIPOD RIFLE M2. A USGI M2 bipod will be of brazed, not welded, construction. The USGI M2 bipods left the factory with a yellow DOD acceptance stamp on the left hand front side of the yoke and a blue letter M, one on the bottom of each leg pad and also on the outside of the right hand clamp. However, the yellow and blue markings tended to wear off with use in the field and are rarely seen on bipods found today.

Both versions of the USGI contractor M2 bipod, 7790688 and 7790833, were initially produced without a sling swivel. M2 bipods marked 7790688 were later manufactured with a sling swivel. Sling swivels were also added to quantities of both versions of M2 bipods while in service through a Modification Work Order or a Direct Support level field modification. M2 bipods with swivels will have a longer pin to secure the swivel to the yoke."