The lap joint flange is practically identical to a slip-on flange except it has a radius at the intersection of the bore and flange face. This radius is necessary to have the flange accommodate a lap joint stub end. Normally, a lap joint flange and a lap joint stub end are mated together is an assembly system.
Specifications:

Lap joint flange
Size: 1/2” to 60”, DN 12mm to DN 1500mm view...
Pressure class: Class 150 to Class 2,500, PN 2.5 to PN 250
Facing: RF / RTJ
Material:view...
Cabon steel: A105, A350 LF2
Stainless steel: A182 F304/F304L/F316/F316L/F321
Alloy steel: F11, F12
Packing: plywood case and plywood pallet
Standards, Dimensions & Weight
ASME/ANSI B16.5 Class 150 LJ
ASME/ANSI B16.5 Class 300 LJ
ASME/ANSI B16.5 Class 600 LJ
ASME/ANSI B16.5 Class 900 LJ
ASME/ANSI B16.5 Class 1500 LJ
ASME/ANSI B16.5 Class 2500 LJ