Strat Tremolo / Whammy Bar M6 Thread

As a rule of thumb here's a good sizing reference:
All USA strats: 10-32 UNF [equivalent 4.82mm]
All Made in Mexico and Made in Japan: M5 [4.80mm thread]
Squier Classic Vibe and Affinity- M5 [4.80mm thread]
Squier Bullets, Deluxes and Standards are usually M6 [5.80mm thread] but sometimes M5
Generic Imports Brands are often M6 [5.80mm thread] but sometimes M5

If you are unsure you can always try an M5 or M6 bolt from a hardware store first, to check the thread of your tremolo/vibrato unit.