How ISO Metric Standards Cut Manufacturing Costs

The ANSI preferred metric sizes are identical to those in the ISO 497 R"20 rounded series selected years ago. The intent of the number series shown is to reduce the number of standard sizes for screw threads, steel plates, steel sheets, round steel bars, lifting capacities, hydraulic cylinder diameters, etc.

The preferred size range from 4 through 40 millimeters may be extended to cover smaller or larger sizes by just multiplying or dividing sizes shown by 10.    For instance, 60-mm sizes would be a preferred choice as would 2.5-mm devices.

For example, the eleven first choice fastener sizes shown in Figure 2 are all metric coarse thread. They are recommended to replace the 53 other thread sizes listed. Furthermore, the four sizes shown in bold are according to the R5 series of preferred sizes shown in Figure 1. The cost reduction becomes substantial when you figure thousands of dollars savings for each unique fastener size that can be eliminated from the product design.

The metric coarse thread pitch is slightly smaller (finer) compared to the customary unified coarse thread pitch. For example; the metric coarse thread M8 has the thread pitch 1.25 mm and the inch thread 5/16 – 18 has the thread pitch 1.41 mm.

Preferred metric, standard metric and customary inch steel plate sizes are shown in Figure 3. It is recommended selections be made from the preferred metric column marked first and second choice. Selection of first choice sizes will further reduce the number of plate sizes from eight to four. This is a huge cost reduction compared with the 19 inch plate sizes that used to be stocked by a large USA company.

You probably do not have to reduce the numbers of ropes used to hold balloons , but the Renard series of sizes gives you a great tool to help cut cost in manufacturing.

Preferred Tolerances

ISO tolerancing standards offer industry a savings opportunity. New software programs make those standards more easily available and can maximize those opportunities and save time as well. Rating basic sizes and tolerances helps reduce the number of hole and shaft sizes specified.

Hole basis fits with hole tolerances identified by ANSI and ISO as H11, H9, H8 and H7 help rationalize on standard cutting tools and gages, whereas shaft basis fits with shaft tolerances h11, h9, h7 and h6 help rationalize on standard round steel bars available in all major industrial countries. See Figure 4.

The ANSI standard and software have ten preferred hole and shaft basis fits ranging from LOOSE RUNNING to FORCE fits shown in Figure 5. It is recommended you use shaft basis fits in most applications since it helps you reduce the cost of cutting tools and gages. However, it may be to your advantage to use shaft basis fits where you have a standard shaft size in the machine with bearings, couplings, sprockets, gears, and other components attached to it. Examples include knitting , printing , and farm machines.

Each preferred fit has the same clearance or interference for hole or shaft basis fit listed on the same line.