Mastery bridge - why are new thimbles needed for American-made guitars after 2012?

[hlamp]

Mastery's website says that its M1 Mastery bridge "requires no modification [on the thimbles] to USA made guitars originally equipped with Fender’s 'floating'-style bridge and vintage spec body thimbles ... The M1 Mastery Bridge and its mounting posts fit all vintage and used American made Fender offset guitars made prior to 2013." But new, replacement thimbles are needed for all American-made Fender offset guitars made in 2013 or later.

What did Fender change to its body thimbles in 2013, to move away from vintage specs?

Did that apply to all of Fender's American-made Jazzmasters and Jaguars from 2013 onward? Like models meant to replicate vintage specs or Fender Custom Shop models.

Is there a rule of thumb for which 2013 or later models require enlarging or filling the body hole to accommodate the replacement thimbles?

[adamrobertt]

Pretty sure it's just a matter of tolerances. The newer thimbles have an ever so slightly too large inner diameter (we're talking thousandths of an inch here) so that the Mastery posts (which are supposed to be snug and immobile) may not be as tight as designed. The only way to ensure the perfect fit is with Mastery thimbles.

They do not require modifying the body, just removing the old ones, as far as I know.

That said I've used stock Fender thimbles with the M1 bridge plenty of times with no ill effects.