My oil pressure sensor is 10x1.25. I'm trying to find a T to add a gauge. I can't find any in the 10mm. Is 1/8" bspt the same size as 10x1.25. Thanks. Mel

 

Short answer NO. British Standard Pipe Thread is the same as SAE pipe thread except for the angle of the threads. BSPT is cut at 55 degrees and SAE Pipe is cut at 60 degrees, but both are tapered.
You will have to get creative for a work around. follow the link below to McMasterCarr they have a 10 mm male to 1/8 pipe adapter, form there you can fit 1/8 pipe but to get the sensor back you have to go 1/8MPT to 10mm female.

 

This is the ready made solution

Jaguar V8 Oil Pressure Adapter - TheJagWrangler