Lewmar Low Profile Hatch Size 40 - 19 5/16 x 19 5/16 in. Flange w/Stay. The sleekly designed Low Profile Hatch is ideal for use on a powerboat. Smaller ventilation hatches are a better fit for sailboats, while the larger sizes can be used as foredeck hatches on smaller to mid size yachts. Note: 1. Hatches should be fitted to a flat surface with a maximum tolerance of ± 1mm. 2. Fastening size for lower frame section use 5mm CSK screws No. 10 UNC 2BA. 3. Fastening size at the hinge section use M6 (1/4").