Enter the shaft/sleeve diameter and packing width to get the exact length to cut, mitred 45° at both ends.
Known Pump (optional)
Measurements
mm
mm
Result
—
Straight length to cut, before the 45° ends are mitred
Ring Centreline ⌀—
Cut Length—
Tip: measure and mark this length along the strip first, then make both 45° cuts — don't try to measure after mitring, since the diagonal faces make a tape measurement ambiguous. If you have a mandrel the same size as the shaft, wrap the packing around it to check the ends meet cleanly before fitting — this is the most reliable way to verify the cut. Cut very slightly long (an extra 1–2mm) and trim to fit rather than cutting short. Stagger the joints of successive rings around the shaft (e.g. 90–120° apart), never stack them in line.
Formula: Cut length = π × (shaft diameter + packing width)
The packing ring's centreline sits one half-width out from the shaft surface all the way round, so its circumference — and therefore the cut length — is based on the shaft diameter plus one full packing width, not the shaft diameter alone.
Ring Around the Shaft
The packing (shaded) sits in the annular gap around the shaft. Its centreline (dashed) is the circle the cut length is measured around — radius = shaft radius + half the packing width.
The 45° Mitred Joint
Cut both ends at 45°, in the same rotational direction, so the two cut faces mate flush when the ends are brought together — like a picture-frame mitre, not a straight butt joint. This stops a single straight-through leak path and lets the joint bed in as the gland is tightened.
The 45° angle is cut through the packing's cross-section, the same way at both ends — it does not add to or shorten the straight cut length calculated above. Measure and mark the cut length along the strip first, then make the two angled cuts.
Further Reading
Trade references used to confirm the formula and cutting method on this page: