Misumi USA Engineering Blog

Surface finish (surface roughness) specifications is a large topic. In fact discussing this topic in length would take at least a few pages. For this blog entry I would simply like to focus on the machined components in the Misumi catalog and point out that these components have surface finish specification (symbol and value) specified in the catalog. Please note that the surface roughness average value (Ra) in the Misumi metric catalog is measured in μm (micrometer-10-6mm) while in Misumi inch catalog it is measured in μin (microinch-10-6in).

See below as the preferred values for Roughness Average (Ra) are given in following table¹.

Metric threads have a different callout then US (inch) threads. Metric threads specify the pitch while US threads specify number of threads per inch.

Example:
Metric
M6 x 1 ( 6- nominal thread diameter in mm, 1mm-distance between threads in mm)

Inch
¼-10 (1/4-nominal thread diameter in inch, 10-number of threads per inch)

Pitch from metric fasteners can be coarse, fine and extra fine. The pitch callout on coarse thread is often omitted. For example, “M6” thread by default stands for coarse thread M6 x 1. Thread call out that includes the pitch “M6x0.75” specifies non-coarse thread (in this case fine thread). Also all threads are right-hand threads unless otherwise specified.

Majority of standards (JIS, ISO, DIN) follow this convention.

For more information about Metric Coarse Threads please see pages 1568/1569 in the 2008 Misumi Metric catalog. Also, see the following links.

Table for Metric Coarse Screw Threads
Table for Metric Fine Screw Threads

When dealing with the Case Hardness of Precision Linear Shafts very often Misumi engineers are asked if our linear shafts are case hardened or through hardened. If you look at the part specification table for Misumi precision linear shafts you will notice that a majority of our shafts are induction hardened. Induction hardening is just one of the ways to achieve case (surface) hardness. Through the induction hardening process the top layer of the shaft is hardened which increases the strength and wear resistance. At the same time the shaft core remains unaffected and material ductility and other physical properties are preserved. Hardness varies with the type of material while effective hardness depth depends on shaft diameter. Values for effective hardness depth can be found in Misumi catalog. See the following links.

Effective hardness depth for metric shafts
Effective hardness depth for inch shafts