This is from my ebay history, but double check sizes.
Clamcleat 3-6 Mm Fishing Accessories Racing Junior Mk1 Hard Anodised 49485
direct replacements, no drilling
Simple ridged v groove holds ropes firmly yet is devoid of any moving parts to break or seize. They are unaffected by the heat generated by a rope surging back through a cleat as well as being suitable for sub-zero temperatures.
Rope size is 3-6mm.
Material - Aluminium - Hard anodised
Dimension - L 82mm, Between Holes 66mm, Width 18mm
Bolt Size - M5
Screw Size 4.8mm
Weight - 35 grms
keepers.
Not sure this is the right size for those cleats, but this is the accessory to search for:
https://www.clamcleat.com/products/accessories/keeper-for-mk2-racing-juniors.htmlhis accessory expands the capability of conventional Clamcleat® rope cleats. The Award Winning CL815 Keeper has been designed to overcome the problem of lines being cleated accidentally as well as improving performance by holding lightly-loaded lines in the jaws of a cleat when mounted upside down. When using a cleat fitted with a Keeper, the operation and performance is completely transformed. The lead-in makes cleating a line easier and there is a satisfying and positive click as the line is released or cleated.
These benefits mean that Clamcleat® rope cleats can now be used on control lines that are adjusted frequently. When a halyard or control line is released from a cleat fitted with a Keeper, the Keeper will stop it falling back into the cleat and re-cleating, for example when dropping a spinnaker during a race or the mainsail when unrigging ashore. A patent has been applied for the innovative Keeper.