What size feeler gauge is used on a snapper z rider?

The correct feeler gauge size for adjusting the tappets on a Nissan Skyline 1988 CA20 engine 2L depends on the clearance that is specified by the manufacturer. Generally speaking, the clearance should be between 0.10mm and 0.15mm. You should use a feeler gauge that is 0.10mm or 0.15mm in size, or one that is slightly thinner than the gap that is specified. If you need further assistance, you can consult a certified mechanic for advice and assistance.

setting is 0 their is no gap

https://www.amplifiedparts.com/products/feeler-gauge-20-sizes
https://www.pakwheels.com/forums/t/need-a-feeler-guage-for-tappet-adjustment/161905
https://www.amazon.com/Armstrong-70-819-Piece-Blade-Gauge/dp/B0012WNIDQ
http://www.skf.com/ph/products/maintenance-products/hydraulic-tools-for-mounting-and-dismounting/hydraulic-tool-accessories/feeler-gauges/index.html
https://www.amazon.com/uxcell-10mm-70mm-Thickness-Plastic-Measuring/dp/B01MRISC7P
https://en.wikipedia.org/wiki/Feeler_gauge

Hi. You will need to purchase a blade feeler gauge. This style gapping tool allows you to add and stack different size feeler gauge sizes and create the size you need.

Check this out David. https://www.partstree.com/parts/snapper/mowers-rear-engine-riding-lawn-mower/381450hbve-84270-snapper-38-rear-engine-rider-14-hp-hydro-drive-series-0/38-deck-sub-assembly

First put the mower on a level surface. Make sure the tires are the correct size and inflated to the proper pressure. Take a ruler and measure from the edge of the deck down to the hard surface. You should see either screw adjustments or perhaps links in a chain. Adjust to where both sides are as close to equal as you can get them. Unequal air pressure in tires or bent blades can be cause of un-even cutting.

model #under seat or hood?

if it's a rear engine rider with a 28 or 30 inch deck the grease fitting is underneath the deck... If it is a rear engine rider, close the fuel off and stand the mower on end but for a short period of time only. This applies to ALL rear engine riders from Snapper up until about 2 years ago when they made a SERIOUS mistake and redesigned them

Check electrode gap with a wire-type feeler gauge. Bend

the outside of the electrode so that only a slight drag is felt on the gauge as it passes between the electrodes. The proper

gap measurement is 0.038-0.043 in. (0.97-1.09 mm).

Complicated and somewhat tedious procedure; try this link to the Volusia Rider's forum:
http://www.volusiariders.com/58-motors-transmissions-drives/194819-how-guide-adjusting-your-valves-101-pics-vid.html

I use the "jpaige" method referred to in this excellent tutorial; I simply could not get the feeler gauge into a position that I was confident with. Good luck!