ASME/ANSI B16.5 Class 900 LJ

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.

ASME/ANSI B16.5 Class 900 LJ

Nominal Pipe Size	Outside Diameter of Flange	Thickness of Lap Joint Min.	Diameter of Hub	Length Through Hub	Bore	Corner Radius of Bore of Lapped Flange	Diameter of Bolt Circle	Diameter of Bolt Holes	Number of Bolts	Approxi-mate Weight kgs
NPS	O	tf	X	Y	B	r	W	I	n
1/2	120	22.3	38	32	22.9	3	82.6	22.2	4	1.69
3/4	130	25.4	44	35	28.2	3	88.9	22.2	4	2.28
1	150	28.6	52	41	34.9	3	101.6	25.4	4	3.41
1 1/4	160	28.6	64	41	43.7	5	111.1	25.4	4	3.89
1 1/2	180	31.8	70	44	50.0	6	123.8	28.6	4	5.41
2	215	38.1	105	57	62.5	8	165.1	25.4	8	9.57
2 1/2	245	41.3	124	64	75.4	8	190.5	28.6	8	13.54
3	240	38.1	127	54	91.4	10	190.5	25.4	8	11.13
4	290	44.5	159	70	116.8	11	235.0	31.8	8	18.96
5	350	50.8	190	79	144.4	11	279.4	34.9	8	31.45
6	380	55.6	235	86	171.4	13	317.5	31.8	12	40.16
8	470	63.5	298	114	222.2	13	393.7	38.1	12	72.66
10	545	69.9	368	127	277.4	13	469.9	38.1	16	105.50
12	610	79.4	419	143	328.2	13	533.4	38.1	20	141.92
14	640	85.8	451	156	360.2	13	558.8	41.3	20	162.02
16	705	88.9	508	165	411.2	13	616.0	44.5	20	199.98
18	785	101.6	565	190	462.3	13	685.8	50.8	20	277.51
20	855	108.0	622	210	514.4	13	749.3	54.0	20	348.93
24	1040	139.7	749	267	616.0	13	901.7	66.7	20	671.17