Recommended for engines revving over 8000rpm.
Each bucket number is an indication of size. The number printed on the bottom side of the bucket is the tenths, and hundredths place indicating the bucket thickness plus 5.00mm. For example: a "42" bucket is 5.42mm thick.
Determining the bucket size you need: Measure the valve lash clearance with your standard lifter or shim and bucket combination using feeler gauges. Recommended intake cam to bucket clearance range is .006 to .010", and exhaust is .008 to .012". Now remove your shim and bucket combination and measure the total thickness with a micrometer. If your clearance was perfect, order that thickness bucket, if your clearance was outside the range, add or subtract the difference from your bucket and shim thickness and order that bucket.
Example: Intake valve cylinder 1 nearest cam gear (1A) measures .004" clearance, and the next over valve on cylinder 1 (1B) measures .009". The bucket and shim thickness for 1A is 0.2109" thick, and the shim and bucket thickness for 1B is .2218". With 25.4mm per inch, 1A is (.2109x25.40)=5.356mm and 1B is (.2218x25.40)=5.634mm. So you would need a #36 bucket for 1A to maintain the same clearance, and a #64 for 1B. Because 1A was under the recommended range, we must use a thinner than recommended bucket. Ideal clearnce on the intake is exactly in the middle of the range or .008". Subtracting our measured clearance from ideal (.008-.004)=.004 is how much we need to subtract from the bucket thickness to get the proper size to achieve ideal clearance. Thus the 1A bucket should be ((.2109-.004)*25.40)=5.255mm or a #26 bucket.
NOTE: Shimless buckets *WILL* work with 3rd generation shim under bucket retainers.