Measure the outside diameter
Use a tape or calipers across the widest coil. Do not use wire diameter or free length as a substitute for OD when checking compressor envelopes.
Why three envelopes
Verified VEVOR US listings on this site publish clasp OD to 6.7 in, hydraulic OD 2.8–7.9 in, and adjustable OD 3.5–11.5 in. StrutIn picks the smallest envelope that contains your measurement.
Lethal energy warning
A compressed coil can kill. Inspect tools, secure the vehicle on rated stands, wear eye protection, and never stand in the spring line. This calculator does not replace manufacturer instructions.
Class ladder on this site
Three verified VEVOR US listings checked 2026-09-10. Availability UNKNOWN until you confirm the live page. Affiliate tracking is pending.