The Betts spacers and adapters are available in various styles.  The bolt patterns are in accordance with TTMA recommended practices and the threads are standard NPT.

Steel and stainless adapters are rated for a MAWP of 75 psi [5.2 bar] and aluminum adapters are rated for a MAWP of 50 psi [3.4 bar].  For single spacer adapter see piping weld flanges Section 40 Page 2B.  All material options may not be available in all sizes and versions.