What do you mean, flange four?
Marine flanges and sealing surfaces
The number of holes is a multiple of 4
Ship standard flange ship GB 10746 - 89
In the past, there were four carry and six carry flanges in the flange standard, which meant only the number of bolted flanges, and the number of bolts in the 4 carry flange was 4 multiples, such as: 4, 8, 16., six, and 6, 12, 18.
