Used a few times, but I rarely had the opportunity to use it. This is a hex bit socket with a grip ring that can hold hex socket head bolts. You can work on hex socket head bolts in deep locations without dropping them. Only the following sizes are available: 3, 4, 5, 6, 8 3/8 (9.5mm) SQ. Overall length 62mm Please check the manufacturer's website for detailed product information. tool tools tool maintenance supplies hand socket Koken tool Yamashita Kogyo Kenkyusho Ko-ken ko-ken