Mixing copper types

I have a 3/4" copper heating line for a baseboard hot water system and need to replace a section of it.

Got the 'type' they had locally and it's thinner than my existing pipe.

Is it okay to mix different thicknesses of pipe. This will be along a below grade concrete block wall behind a wall in a bathroom (if that makes any difference).

Thanks folks...new here and I'll bet I'll find a lot of help!

Doug in NJ

tubing

The thin type "M" tubing is the standard for baseboard heating so you are fine. The only tubing that would not be acceptable would be ACR refrigerant tubing because that is even thinner.