The Siemens 5SL6240-6CC is a 2-pole miniature circuit breaker rated 400 V with a 6 kA breaking capacity, B-curve trip characteristic, and 40 A current rating. It's a current-production Basic Devices series MCB — still in active manufacture, so no scavenger-hunt sourcing needed for a BOM line. At 40 A per pole, it'll handle a decent sub-panel feed or a group of smaller branch circuits. The 2-pole form factor means it switches both line and neutral (or two phases) simultaneously — typical for single-phase final circuits where you want the neutral isolated on a fault.
RoHS compliant since 01-06-13, so it's good for EU and UK markets without an exemption expiry headache. Product class B means returns are restricted — contact your Siemens partner for any return authorization. Not a showstopper, but worth noting if you're stocking spares and might need to send one back.