Converting 7/8 into metric gives precise dimensions for engineering, construction, and manufacturing tasks. Understanding this fraction in millimetres helps standardize measurements across global projects.
Use the reference table and guidance below to apply 7/8 inch metric values reliably in technical drawings, procurement, and field work.
| Imperial Value | Exact Metric Conversion | Rounded Metric (1 dp) | Common Use Cases |
|---|---|---|---|
| 7/8 inch | 22.225 millimetres | 22.2 mm | Pipe threads, shaft collars, sheet metal |
| 1 7/8 inch | 47.625 millimetres | 47.6 mm | Bolt heads, frame widths, panel cutouts |
| 2 7/8 inch | 73.025 millimetres | 73.0 mm | Mechanical mounts, tooling bases |
| 5 7/8 inch | 149.225 millimetres | 149.2 mm | Screen diagonals, display bezels |
Practical 7/8 to Metric Conversions
Use these direct conversions when specifying parts or reading technical drawings that mix imperial and metric values.
- 7/8 inch = 22.225 mm, often rounded to 22.2 mm or 22 mm depending on tolerance.
- For lengths like 1 7/8 inch, add one inch (25.4 mm) to the base conversion, giving 47.625 mm.
- Multiply the inch value by 25.4 to convert any 7/8 increment precisely without memorising tables.
- Always verify rounding against project tolerance, especially for press fits and threaded assemblies.
Machine Design and Tolerances
In machine design, specifying 7/8 inch dimensions in metric requires attention to tolerance bands and fits.
Standard Tolerance Guidelines
For drilled holes based on 7/8 inch shafts, use H7/g6 or H8/g7 fits to mirror imperial clearance standards.
When converting press-fit dimensions, maintain the same grade number to avoid unexpected interference or play in assemblies. h3>Material Expansion Considerations
Thermal expansion calculations should use the exact 22.225 mm value rather than rounded figures for high-precision polymer or metal parts.
Manufacturing and Procurement
Suppliers and machining shops commonly request metric equivalents for imperial prints, making 7/8 inch conversions essential.
- Request stock sizes close to 22 mm, 47.6 mm, or 73 mm to minimise waste and lead time.
- Confirm thread pitches, such as 1 mm per thread for coarse metric bolts approximating inch-based threads.
- Verify surface finishes and tolerances with suppliers when moving from imperial to metric selections.
- Document converted values in both imperial and metric on purchase orders to prevent misinterpretation.
Field Installation and Inspection
Onsite teams rely on clear metric markings when verifying that components match converted specifications.
- Use digital calipers or gauge pins marked in millimetres to check 22.225 mm shoulders and seats.
- Align bores and shafts using adjustable fixtures that allow fine tuning around the 22 mm nominal size.
- Compare machined parts against certified measurement tools traceable to national metrology standards.
Optimising Technical Documentation
Clear documentation prevents rework when teams switch between imperial sources and metric tooling.
- List dimensions in both systems on drawings and specifications until full metric adoption is achieved.
- Highlight converted critical dimensions, such as 22.225 mm shaft diameters, with notes on allowable tolerances.
- Train staff to mentally map common fractions, including 7/8 inch, to their primary metric equivalents.
- Schedule periodic audits of supplier drawings to ensure consistent and accurate unit usage across projects.
FAQ
Reader questions
How do I convert 7/8 inch pipe threads to metric?
Treat 7/8 inch as 22.225 mm and pair with a compatible metric thread pitch, such as 1.5 mm or 2 mm coarse, depending on the system standard.
What is 7/8 inch in millimetres for machining purposes?
For machining, use 22.225 mm as the reference and apply your required tolerance band, commonly h7, g6, or m6.
Can I use a 22 mm bolt instead of 7/8 inch?
Yes, a 22 mm bolt is a practical substitute, but verify thread fit and grip length to match the original design intent.
Is 7/8 inch exactly 22.2 mm in all standards?
No, 22.2 mm is a rounded value; the exact conversion is 22.225 mm, which may matter for tight tolerance applications.