The primary gear is a very abused part of the transverse A-series engine, and it's thrust clearance is absolutely critical for longevity. The thrust clearance is taken up by these bronze shims that sit on the crankshaft flange. Endfloat should be between .003" and .006", but race applications can add an extra cushion. 
 
Available in the following thicknesses: 
.112" to .114" - Black
.114" to .116" - Red
.116" to .118"- Blue
.118" to .120" - Green
.120" to .122" - Yellow
.122" to .124" - White
 
Not returnable.