I believe the 2 standard size holes for valve stems are 0.453" and 0.625", There is also a 0.327" size which is less common. There are they common automotive type that are made of rubber and pull into place from the inside of the rim and then there are screw in types that are all metal and have a rubber gromet/washer on the inside and outside and are secured via a nut that threads onto the metal valve stem shaft, On both my Kubotas the wheels have the screw in types of valve stems. I believe the screw in types are used where there is a danger of the valve stem being damaged by something coming into contact with it such as mud,brush,tree limbs,rocks,sand gravel etc.
Below is a link which shows some of the screw in types, There are low profile and right angle. I like the low profile because it reduces the chance of the valve stem getting snagged or damaged.
Scroll down to the bottom of the page for the valve stems, Site provided for size info only and not an endorsement of any particular product or vendor
Some older tubed tires may have a larger hole