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BS 1640-3:1968
Specification for steel butt-welding pipe fittings for the petroleum industry. Wrought carbon and ferritic alloy steel fittings. Metric units (British Standard)
Dimensions and tolerances, materials, methods of manufacture, pressure/temperature ratings, marking, inspection, tests for seamless and fabricated fittings: 45$0D long radius elbows, 90$0D long and short radius elbows, 90$0D long radius tangent elbows, long and short radius return bends, equal and reducing tees, concentric and eccentric reducers, caps and lap-joint stub ends, of sizes 19 mm to 609.5 mm. Welding-neck flanges not included.
British Standards Institution [bsi]