noun
hexagon socket head; Allen socket head
Technical term for a screw or bolt head with a hexagonal recess, driven by a hex key (Allen wrench).
このボルトは六角穴付きなので、六角レンチが必要です。
This bolt has a hexagon socket head, so you need a hex wrench.
六角穴付きボルトを締める。
Tighten the hex socket head bolt.
六角レンチ is the tool (hex wrench), while 六角穴付き describes the fastener head type.
Compound of 六角 (hexagon) + 穴 (hole) + 付き (attached, with). Describes a fastener head with a hexagonal recess.