The 16/100 marking is the dual US/European size: 16 (US) and 100 (EU).

A 100 (EU) needle has a shaft diameter of about 1.0 mm and is intended for mediumheavy to heavy fabrics such as denim, canvas, upholstery, and similar weights

As regular/sharppoint overlock needles, DCx1 in size 16/100 are suited to seaming and edgefinishing heavier woven fabrics on serger/overlock machines.