I prefer the use of a caliper for measurements of 1 inch or less. Millimeter rulers or OK for longer measurements.
When you provide photos of your feed-slot from the inside & out angles I will know what extra information is needed to build you a custom MastGate
This internally mounted Self-Closing gate is for the A & B mast profiles with Track Depths of 3/4" or more.
Best for single-handed sailing.
Single & Dual Hinged gates work with all mast profiles.
Single & Dual (Fixed) non-tethered gates fit all mast profiles.
Removable nylon rivet holds the gate in position. Pull center pin up to release plate.
Optional addition of a D-Ring for tethering to mast or your finger to prevent dropping.