Two proximity sensors with the same 8 mm sensing distance can be incompatible with the same mounting plate. The difference sits in fields the buyer did not state, and each supplier then picks a different part number.
Start with mounting: flush or non-flush. A flush sensor can sit inside metal, while a non-flush version needs a clear zone around the sensing face and usually offers a longer distance for the same housing.
Target material comes second. Inductive sensors are rated against mild steel; aluminium, brass and stainless steel reduce the usable distance, and the quotation should state the reduction factor rather than leaving it to trial and error.
Output type, supply voltage and connection complete the list. NPN versus PNP must match the controller input, and a 2 m cable versus an M12 connector changes both spares strategy and installation time.