The 240SX/S13 coilovers are a popular upgrade for the 300ZX/Z31 chassis, whereas the later model 240SX struts are too tall, the earlier ones are just the right size. They require a single additional hole to be drilled for the top hat to fit, and requires these adapter sleeves at the bottom to work with the OEM mount.
This kit includes 2 hard anodized aluminum sleeves, they mimic the 240SX mounting stud, but as every coilover is manufactured with slight dimensional differences, some basic modification will be required. Trimming of the sleeves at one end or both will be necessary, as will grinding down the protrusions on the OEM mounting bracket that were designed for a small diameter tube only. Reuse the original Nissan shock bolt and nut when mounting.
How it requires trimming will depend on the coilover models used, some are too narrow and will need the thinner end trimmed, while others are longer requiring the large end trimmed, a very few will need a little from each end removed. It is also possible the coilover bushing sleeves have a large/wide taper, and will accept the adapter sleeves from one direction only, test the adapter from both directions to see which way sits most comfortably. In very rare cases, an M20 washer may be required to slip over the narrow end before being installed.