Standard hammer union sizes include 1", 2", 3", 4", 5", 6", 8", 10", and 12" nominal pipe sizes. The most common are 2" fig 1502 and fig 2202 for high-pressure sour gas service, and 4" fig 602 and fig 1002 for medium-pressure applications https://globalsealstech.com/product/hammer-union-seal-2/