Product Quantity Minimum 1
Product Quantity Maximum 0
Product Quantity Units 1

Translation - min - what is the minimum that can be ordered at one time.
max - what is the maximum that can be ordered at one time/one order
quantity units - what it the unit of sale e.g. cars or furniture would be sold in units of 1, nuts, bolts or nails might be in units of 100 or 500.

Product Quantity >0, whatever you have in stock.