Which one should the drawing call out?
Brass when the housing is a thermal probe in a compatible coolant, stainless when corrosion resistance, strength or a galvanic couple rules it out. The choice changes the entire route, not just the material line on the drawing.
The comparison that matters
- Thermal response: brass wins; it conducts heat away from the sensing element faster.
- Corrosion: stainless wins, particularly against chloride-bearing or aged coolant.
- Machinability: brass machines cleanly for threads and sealing faces; stainless needs more care and different tooling.
- Forming: brass runs comfortably in a progressive tool; stainless draws with more springback and more tooling attention.
- Cost: brass price follows copper, stainless follows nickel and molybdenum - both are volatile, which is why the quotation states the material basis.
What to state
The coolant chemistry, the operating temperature range, the thread or sealing interface, and whether the housing carries any structural load. Those four answers settle the grade without a trial.
Grade, wall thickness and tolerance are confirmed against the customer drawing. Batch heat treatment, slow wire cutting, passivation, electropolishing, plating, phosphating and coating are placed with qualified external processors and disclosed on the inspection plan. The quality system is ISO 9001:2015 with controls aligned to IATF 16949 requirements.