From the reference below:
"All boxing gloves are cut, assembled, stitched, stuffed, and finished by hand. The manufacture of a glove begins with a pattern of the individual pieces. While every manufacturer has a different pattern, the basic pieces are the palm, which is cut with a slit down its middle that will eventually form the closure section of the glove; the knuckle area, which is always made from a single piece of leather to avoid seams; the thumb, which is made from two halves; the CUFF, which is cut as a wide strip; and a thin strip that will be folded over and sewn onto the edge of the CUFF and the closure area to finish the glove. The knuckle piece is cut to be larger than its finished size so that space is left for stuffing."