To help USA customer struggling with their speed running too fast we have made 5% smaller one . So if yours is running too fast you can use this one to keep your deck in range .
As a rough guide to help customer choose between the 2.5% and the 5% smaller pulley
If your your speed when the deck is at cold and just creeps faster when the setting is on MAX – then choose the 2.5% one
If your deck is running fast when the MAX – is on and the speed is running faster than creeping then use the 5% version