6m6 dowel pin (+4/+12), Hole H7 (+0/+12) is preferred for sliding (tight) to tapping (light press) fit. If you want a good press fit for an 6m6 dowel pin you will have to go with a hole size 6P7 = 6 -8/-20. Easy to remember P/p stands for "Press" on dowel pins. If you would like to use a 6H7 reamer (common size) than stone it lightly to make certain you get the type of press fit you want. A brand new 6H7 reamer comes with a tolerance of +5/+10. A brand new 6P7 reamer has a tolerance of -10/-15.