This is a .030" shim made of a special copper material designed to wear faster than the block. Low cost insurance item that should be replaced with every engine rebuild.
Cam Gear Wear Plate
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SBC cam gear wear plate
Part Number: 6011 S/B Chevy Cam Gear Wear Plate$6.00... more info -
BBC cam gear wear plate
Part Number: 6012 B/B Chevy Cam Gear Wear Plate$6.20... more info -
.155 thick brass thrust washer for S/B.
Part Number: 6016 .155" thick brass Cam Gear Washer for B/B.$22.50... more info