Summary of Slot Machine Buttons
Bets the maximum number of coins from your credits to play all available rows (and bets) on a multi-coin machine. You can only use this option if you have enough money in your bankroll to cover the maximum bet amount.
You can make a maximum coin bet during play by:
Clicking Bet Max (when it is lit).
Pressing the letter M on the keyboard.
Choosing Bet Max from the Actions menu.