O Scale 1:43.5 (4.5″/5″ pipe)
O Scale 1:48 (5″/6″ pipe)
O Scale 1:64 (7″/8″ pipe)
This coupling is part of a set of pipe fittings that are designed to connect to Evergreen #224 tubing. This tubing has an Outside Diameter (O.D.) of 0.125″/3,2mm and an Inside Diameter (I.D.) of 0.069″/1,8mm.
Evergreen tubing has a ‘Nominal’ ID. of 0.069″/1,8mm .. meaning don’t try to force the fitting but if necessary ream the tubing to the correct ID
For NPS ⅛ to 12, the NPS and OD values are different. For example, the OD of an NPS 12 pipe is actually 12.75 inches. For NPS 14 and up, the NPS and OD values are equal. In other words, an NPS 14 pipe is actually 14 inches OD. To a large extent such variations in size can be ignored by we modelers as the slight difference at the scale we model is scarcely noticeable.
The chart shows that for example if you are modeling in 1:48 then that 0.125″ O.D. of the tubing would be 6″. Look down the column and this is in the 5″ to 6″ (nominal) pipe O.D. – actual being 5.563″ and 6.625″. The fittings are therefore useful in 1:43.5 and 1:64 as all those these fittings all have 8 bolt flanges.