The right tool!
This handy pocket-sized tool fits all deck plate caps: slotted, raised lug, spaced hole, and star (winch handle) type caps. The tool also has common hex sizes: 5/16" (8mm) for hose clamps and 7/16" (11mm) for 1/4" (6mm) bolts. Other features include a shackle key, flat screwdriver, and bottle opener.
A wide, flat edge gives good hand leverage when using the shackle key. The hexes are close to the edge for ease of use, and the screwdriver stands out in relief for working in tight places. Constructed of specially hardened stainless steel. Will not corrode or break.