A familiar metric label can be a rounded representation of an inch size. That distinction matters when a drawing or purchase document needs an exact nominal dimension.
Convert first, then identify the controlling dimension
One inch is exactly 25.4 mm. The conversions for BOYA’s three featured inch designations are:
| Inch designation | Exact conversion | Common metric label |
|---|---|---|
| 5/32 inch | 3.96875 mm | 3.969 mm |
| 3/16 inch | 4.7625 mm | 4.763 mm |
| 1/4 inch | 6.35 mm | 6.35 mm |
The last column is a convenient product label with up to three decimal places. It is not a tolerance, inspection result or a new acceptance limit.
Make the drawing unambiguous
When preparing an RFQ, identify whether the inch dimension or the metric dimension controls. Do not assume that a rounded display value automatically replaces the nominal dimension on the engineering drawing.
State the permitted tolerance or precision grade under the agreed standard. Also include any ball gauge or lot requirements specified by your engineering team. If the drawing and purchasing system use different units, resolve that difference before order confirmation.
Avoid ambiguous quantity and size fields
Always include units. A list containing only “4.763 / 100000” can be misread. Separate the nominal dimension, grade, order quantity and quantity unit into clearly labelled columns.
For repeated orders, keep the approved drawing revision and part number with the purchase record. That makes it easier to notice when a dimensional description has changed.
BOYA’s featured dimensions
Our G10 chrome steel ball page highlights the three common metric labels above. Other sizes can be discussed through an enquiry, and the supply specification must be confirmed before an order.