The finer the tolerances required, the more costly the part. M2 is the normal tolerance band for industrial parts. Bear in mind that rubber is elastic and easily accomodates variation. M1 tolerances require the moulding process to be designed around dimensions for example by reducing the number of cavities or reducing injection speeds and will usually mean increase costs.
Tolerances for moulded products to ISO 3302 1995 (BS 3734)
Table classes M1 (Precision) and M2 (Commercial).
F = Fixed dimensions (across cavity area)
C = Closure dimensions (dimensions affected by split lines)
The lowest cost of quality is obtained when it is built into the development process by agreement. Inspecting it in at a later date is relatively expensive.
Mech is approved to ISO 9002 and many other standards.