What size hole for sliding fit?

[Wongster]

Hi guys,

Me with my questions again.

I'm helping someone to machine a clamping post for his tennis racket stringing machine.  The stainless steel shaft that the clamp post needs to go on is 11.97mm in diameter.  It must slide on the shaft easily but without noticeable wobbly.  

I made the part and drill through with a 12mm HSS drill.  The part couldn't go on the shaft.

What size should I drill the hole for the part to slide on easily and yet without noticeable wobbly?

Regards,
Wong