Free length is the end-to-end length of a compression spring when it is unloaded. A tolerance tells you how far the manufactured part may vary from its nominal value, but the allowed amount can depend on the exact product and series. This table collects selected values from Lee Spring stock product pages and keeps each tolerance tied to its published part number. It is an example lookup for those items, not a universal spring tolerance chart.

Compression Spring Free Length Tolerances

Find the complete Lee Spring part number first. Then compare the listed nominal free length and tolerance with the table row. For part CI012B03M, the product page lists a 6.35 mm free length and a ±0.46 mm tolerance. The corresponding dimensional interval is 5.89 to 6.81 mm, using the tolerance shown for that item. This calculation describes the nominal band; it does not replace a current specification sheet or acceptance plan.

Part codes matter because similar looking springs can belong to different series, use different materials and have different dimensions. The table includes instrument, standard and Lite Pressure series examples. The values are read from product-specific Lee Spring pages, so a row for one code must not be assigned to a different spring merely because its nominal length is close.

Before inspection, confirm whether the drawing defines free length in the unloaded state and how the spring should be positioned. Measure without applying compression or tension, keep the end conditions consistent with the product definition, and use a calibrated instrument with suitable resolution. If the spring has hooks, legs or other features, establish whether the stated free length includes them by checking the exact product drawing.

Length variation is separate from spring rate and load tolerance. Two springs can meet a free-length band and still differ in force at a working height if their rate or load tolerance is not also controlled. Likewise, compression below solid height can cause permanent set, changing the spring after the measurement. This lookup covers free length only; it says nothing about fatigue life, load, rate, solid height or dimensional clearance.

Use the manufacturer’s product page to locate the current specification sheet before purchasing or accepting parts. Stock listings and product configurations can change, and customer-specific orders may have a build specification that differs from the public page. If the purchase order or drawing has a tighter tolerance, that requirement governs the inspection decision.

A common mistake is treating the tolerance in one product listing as a size-based rule for every spring in the catalog. The Lee Spring pages are tied to specific stock items. Another is reading “free length” as the compressed working height. Measure the spring in its unloaded position and use the correct drawing definition.

For a new design, allow the full tolerance band in the assembly stack and check the spring’s operating length separately. Consider guide alignment, end support, buckling, coil contact and the tolerances of the surrounding parts. If the assembly depends on a narrow spring length or force window, request a controlled specification from the manufacturer and verify the lot against that requirement.

When recording an inspection, note the part code, lot, measured free length, instrument and measurement setup. This makes a borderline result traceable to the correct product tolerance and prevents a tolerance from being copied between visually similar springs. For critical assemblies, include the free-length requirement and spring series on the purchasing specification.

Sources

Each row links directly to its Lee Spring stock product listing, which reports the nominal free length and item-specific tolerance. See also Lee Spring’s engineering notes and tolerances for general scope guidance.