57) What is the angle of countersink tool used on holes to be threaded?

58) What is the formula to calculate the blank size of external thread (where p=pitch and d=depth)?

59) Which type of thread, the crest and roots are rounded to form a semi circle?

60) What 5 denotes in grinding wheel specification 41A46H5U8?

61) Which type of bonded wheel is used in foundries for dressing castings?