> I wonder if the "C5" refers to a set or class of tolerances, then. The "4.8" > would refer to the diameter and thread spacing as normal for metric > fasteners. > > Jim >
No, the 4.8 refers to a fastener's property class, which in FFU screws would be the grade. Each metric Class symbol consists of two numbers separated by a period. The first number is 1/100 of the nominal tensile strength in N/mm2 (newtons per square millimeter. The second number is 10 times the ratio of nominal yield stress to nominal tensile strength. For example, a Class 4.8 bolt has a nominal tensile strength of 400 N/mm2 and a nominal yield stress of 320 N/mm2 (8 times 400 divided by 10). http://www.stealth316.com/2-3s-fastener-tips.htm http://euler9.tripod.com/bolt-database/22.html I'm not sure what the C5 means. Here is info on tolerancing; Default metric fastener thread tolerance class. If thread tolerance class designation (e.g., "-6g") is omitted (e.g., M10 x 1.5), it specifies "medium" thread tolerance, which is 6H/6g. The 6H/6g fit is the standard ISO tolerance class for general use. I hope this answers your question
