About 145|Tellurium copper (99.5% copper, 0.5% tellurium). The best-machining copper alloy, period. Machinability rating is around 85 versus about 20 for
C110. Tellurium breaks chips into short, clean fragments instead of the bird’s-nest razor wire you get with pure copper. Surface finish is dramatically better. Tool life doubles or triples. Electrical conductivity is 93% IACS — a small tradeoff for massive machinability gains. If your part needs copper and gets machined, C145 should be your first choice unless the 7% conductivity loss or the tellurium content is a deal-breaker. Used for electrical connectors, motor parts, fasteners, and anything turned from copper bar. Compare to C110 (higher conductivity, miserable to machine) and C360 brass (even better machinability but completely different conductivity).
