That is a shim. Honda sells about 20 different sizes. You need to install the correct size. If you put the tranny back together without it bad things will happen. Did you recently switch tranny casings? Look into a helms manual and measure the clearance and order the correct shim and you will be good to go.
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Don't bother giving me "rep", I won't return it and I think it is stupid.
Gracie Barra Clearwater
Gyms in Clearwater, St. Pete and Port Richey
pm me if you are interested in trying a free class at any of the gyms.