Bass machine heads- lighter is tighter.

[Simon Barden]

Traditional Fender large hole size is 11/16", which is around 17.3mm.

Hipshot do some lovely ultralight bass machine heads (HB6) available with Y, clover and lollipop style heads, but they are expensive. https://store.hipshotproducts.com/ca...t_detail&p=108

There is also a licensed (Asian made) version that's still relatively expensive for a set, but almost half-the price. https://store.hipshotproducts.com/ca...t_detail&p=405

I've got the US version on a Lakland skyline P-bass (plus an added x-tender) and they are very nice indeed.

You'd need the 1/2" version (fits an 11/16" hole) rather than the 3/8" version.

Unfortunately they don't seem to be sold in Australia, so it would have to be an internet order.