Spectacle Blind Flange Dimensions

Quick Reference

Spectacle blinds (figure-8 blinds), flange spades, and ring spacers are pipeline isolation devices per ASME B16.48. They provide positive isolation for maintenance, inspection, or shutdown-a cost-effective alternative to isolation valves. Available in sizes 1/2” to 24” and Classes 150-2500.

Spectacle Blind

What Is a Spectacle Blind (“Figure-8”)

A spectacle blind consists of two metal discs connected in the middle: one solid plate (blind) and one ring (spacer). Rotating the device switches between blocking flow (blind) and allowing flow (spacer).

Position	Function
Blind side in	Complete flow isolation for maintenance, inspection, or shutdown
Spacer side in	Normal operation-unrestricted flow through pipeline
Rotation	Quick changeover without removing device from flanges

Advantages: Reduces downtime vs. removing pipe sections; provides positive isolation (physical barrier); suitable for frequent switching between operation and maintenance.

Pro Tip

When installing spectacle blinds, always use two new gaskets - one on each side of the device. Reusing gaskets from the original flange joint leads to leaks. For rotating spectacle blinds, pre-install both gaskets so the new gasket is already in position when you rotate to the other side.

Materials and Manufacturing

Spectacle blinds are produced from steel plates and available in forged material grades:

Material	Grade	Application
Carbon steel (high-temp)	ASTM A105	Standard service to 800°F
Carbon steel (low-temp)	ASTM A350 LF1/LF2/LF3	Service to -50°F
Stainless / Alloy	ASTM A182 (various)	Corrosive or high-temp service

Carbon steel blinds are manufactured from a single piece; alloy/stainless blinds are typically welded from 2-3 pieces.

Visual Identification

One disc is always visible outside the pipeline: ring visible = pipeline closed; solid disc visible = pipeline open. For separate spades/spacers, handle holes indicate position (1 hole = spade, 2 holes = spacer).

Spectacle Blind Types

Face Type	Description	Gasket	Application
FF (Flat Face)	Flat disc surface	Flat face gaskets	Low pressure
RF (Raised Face)	Additional thickness on face	Spiral wound	General service
RTJ (Ring Joint)	Machined groove on face	Metal ring	High P/T

Spectacle Blind Dimensions in mm ASME B16.48

CLASS 150

Class 150 Spectacle blind dimensions in mm

Spectacle Blind NPS Dimensions Class 150	A	B	C	t	W
1/2	45	16	60	3	38
3/4	54	21	70	3	38
1	64	27	80	3	38
1¼	73	42	90	6.4	38
1½	83	48	100	6.4	38
2	102	61	120	6.4	51
2½	107	73	140	6.4	51
3	133	89	150	6.4	64
3½	159	102	175	9.7	64
4	172	114	190	9.7	64
5	194	141	215	9.7	76
6	219	168	240	12.7	76
8	276	219	300	12.7	76
10	337	273	360	15.7	102
12	406	324	430	19.1	102
14	448	356	475	19.1	108
16	511	406	460	22.4	108
18	546	457	580	25.4	114
20	603	508	635	28.4	121
24	714	610	750	31.8	140

CLASS 300

Class 300 Spectacle blind dimensions in mm

Spectacle Blind NPS Dimensions Class 300	A	B	C	t	W
1/2	51	16	65	6.4	38
3/4	64	21	80	6.4	38
1	70	27	90	6.4	38
1¼	79	42	100	6.4	38
1½	92	48	115	6.4	38
2	108	61	125	9.7	51
2½	127	73	150	9.7	51
3	146	89	170	9.7	64
3½	162	102	185	12.7	64
4	178	114	200	12.7	64
5	213	141	235	15.7	76
6	248	168	270	15.7	76
8	305	219	330	22.4	76
10	359	273	385	25.4	102
12	419	324	450	28.4	102
14	483	356	515	31.8	108
16	536	406	570	38.1	108
18	594	457	630	41.1	114
20	651	508	685	44.5	121
24	772	610	810	50.8	140

CLASS 600

Class 300 Spectacle blind dimensions in mm

Spectacle Blind NPS Dimensions Class 600	A	B	C	t	W
1/2	51	16	65	6.4	38
3/4	64	21	80	6.4	38
1	70	27	90	6.4	57
1¼	79	37	100	9.7	57
1½	92	43	115	9.7	67
2	108	55	125	9.7	57
2½	127	67	150	12.7	67
3	146	83	170	12.7	67
3½	159	96	185	15.7	76
4	191	108	215	15.7	76
5	238	135	265	19.1	86
6	264	162	290	22.4	86
8	318	212	350	28.4	95
10	397	265	430	35.1	105
12	454	315	490	41.1	105
14	489	346	525	44.5	114
16	562	397	605	50.8	124
18	610	448	655	53.8	133
20	679	497	725	63.5	133
24	787	597	840	73.2	152

CLASS 900

Class 900 Spectacle blind dimensions in mm

Spectacle Blind NPS Dimensions Class 900	A	B	C	t	W
1/2	60	16	80	6.4	38
3/4	67	21	90	6.4	41
1	76	27	100	6.4	57
1¼	86	37	110	9.7	57
1½	95	43	125	9.7	67
2	140	55	165	12.7	57
2½	162	67	190	12.7	67
3	165	83	190	15.7	67
4	203	108	235	19.1	76
5	244	135	280	22.4	86
6	286	162	320	25.4	86
8	356	212	395	35.1	95
10	432	265	470	41.1	105
12	495	315	535	47.8	105
14	518	346	560	53.8	114
16	572	397	615	60.5	124
18	635	448	685	66.5	133
20	696	497	750	73.2	133
24	835	597	900	88.9	152

CLASS 1500

Class 1500 Spectacle blind dimensions in mm

Spectacle Blind NPS Dimensions Class 1500	A	B	C	t	W
1/2	61	16	80	6.4	38
3/4	67	21	90	9.7	41
1	76	27	100	9.7	64
1¼	86	35	110	9.7	64
1½	95	41	125	12.7	70
2	140	53	165	12.7	70
2½	162	63	190	15.7	76
3	172	78	205	19.1	76
4	206	102	240	22.4	89
5	251	128	290	28.4	89
6	279	154	320	35.1	89
8	349	203	395	41.1	102
10	432	255	480	50.8	114
12	518	303	570	60.5	114
14	575	333	635	66.5	127
16	638	381	705	76.2	133
18	702	429	775	85.9	146
20	752	478	830	95.3	152
24	899	575	990	111.3	178

CLASS 2500

Class 2500 Spectacle blind dimensions in mm

Spectacle Blind NPS Dimensions Class 2500	A	B	C	t	W
1/2	67	16	90	9.7	38
3/4	73	21	95	9.7	41
1	83	27	110	9.7	64
1¼	102	35	130	12.7	64
1½	114	41	145	15.7	70
2	143	53	170	15.7	70
2½	165	63	195	19.1	76
3	194	78	230	22.4	76
4	232	102	275	28.4	89
5	276	128	325	35.1	89
6	314	154	370	41.1	89
8	384	198	440	53.8	102
10	473	248	540	66.5	114
12	546	289	620	79.2	114

ASME B16.48 covers dimensions, marking, P/T ratings, materials, and testing for line blanks NPS 1/2 to 24 for ASME B16.5 flanges (Classes 150-2500).

Common Mistake

Installing a Class 150 spectacle blind in a Class 300 system because “it fits between the flanges.” The thickness calculation for spectacle blinds depends on pressure rating - a lower-class blind may bulge or even rupture under higher pressure. Always match the blind’s pressure class to the system design pressure, not just the flange dimensions.

Flange Spade and Ring Spacer

Flange Spade (Paddle Blank)

A flange spade is a solid disc inserted between flanges to isolate a pipeline section. Also called “blanking spade,” “single-blind,” “blank,” or “paddle blind.” The spade has a handle with one signaling hole.

Ring Spacer

A ring spacer is a disc with a center hole matching the pipe bore. It fills the gap between flanges when the spade is removed, allowing flow. The spacer handle has two signaling holes.

Spade/Spacer vs. Spectacle Blind

Device	Description	When to Use
Spectacle blind	Combined spade + spacer; rotates in place	Adequate clearance for rotation
Separate spade/spacer	Individual devices swapped in/out	Space constraints prevent rotation

Space Requirements

Spectacle blinds require clearance for rotation (approximately disc diameter + handle length). In congested piping, use separate spades and ring spacers instead.

Field Note

Always paint or mark spectacle blind handles with high-visibility colors - during turnarounds, operators need to quickly identify which devices are in the blind position. In one plant, we color-coded all handles: red for blind-in (isolated), green for spacer-in (flowing). This simple visual system prevented several near-misses during re-commissioning.

Flange Spade and Ring Spacer Dimensions ASME B16.48

CLASS 150

(Dimensions in mm)

Flange spade and ring spacer

NPS	A	B	C	t	W
1/2	45	16	126	3	32
3/4	54	21	131	3	32
1	64	27	136	3	32
1¼	73	42	145	6.4	32
1½	83	48	145	6.4	32
2	102	61	155	6.4	32
2½	107	73	170	6.4	32
3	133	89	170	6.4	32
3½	159	102	202	9.7	38
4	172	114	202	9.7	38
5	194	141	225	9.7	38
6	219	168	225	12.7	38
8	276	219	267	12.7	38
10	337	273	322	15.7	44
12	406	324	357	19.1	44
14	448	356	378	19.1	44
16	511	406	410	22.4	44
18	546	457	427	25.4	51
20	603	508	455	28.4	51
24	714	610	512	31.8	51

CLASS 300

NPS	A	B	C	t	W
1/2	51	16	129	6.4	32
3/4	64	21	136	6.4	32
1	70	27	139	6.4	32
1¼	79	42	150	6.4	32
1½	92	48	150	6.4	32
2	108	61	158	9.7	32
2½	127	73	177	9.7	32
3	146	89	177	9.7	32
3½	162	102	205	12.7	38
4	178	114	205	12.7	38
5	213	141	240	15.7	38
6	248	168	240	15.7	38
8	305	219	281	22.4	38
10	359	273	333	25.4	44
12	419	324	363	28.4	44
14	483	356	395	31.8	44
16	536	406	422	38.1	44
18	594	457	450	41.1	51
20	651	508	480	44.5	51
24	772	610	540	50.8	51

CLASS 600

NPS	A	B	C	t	W
1/2	51	16	129	6.4	32
3/4	64	21	136	6.4	32
1	70	27	139	6.4	32
1¼	79	37	150	9.7	32
1½	92	43	150	9.7	32
2	108	55	158	9.7	32
2½	127	67	177	12.7	32
3	146	83	177	12.7	32
3½	159	96	211	15.7	38
4	191	108	211	15.7	38
5	238	135	248	19.1	38
6	264	162	248	22.4	38
8	318	212	288	28.4	38
10	397	265	352	35.1	44
12	454	315	381	41.1	44
14	489	346	398	44.5	44
16	562	397	435	50.8	44
18	610	448	459	53.8	51
20	679	497	493	63.5	51
24	787	597	547	73.2	51

CLASS 900

NPS	A	B	C	t	W
1/2	60	16	134	6.4	32
3/4	67	21	137	6.4	32
1	76	27	142	6.4	32
1¼	86	37	151	9.7	32
1½	95	43	151	9.7	32
2	140	55	174	12.7	32
2½	162	67	186	12.7	32
3	165	83	186	15.7	32
4	203	108	217	19.1	38
5	244	135	259	22.4	38
6	286	162	259	25.4	38
8	356	212	307	35.1	38
10	432	265	370	41.1	44
12	495	315	401	47.8	44
14	518	346	412	53.8	44
16	572	397	440	60.5	44
18	635	448	471	66.5	51
20	696	497	501	73.2	51
24	835	597	571	88.9	51

CLASS 1500

NPS	A	B	C	t	W
1/2	61	16	135	6.4	32
3/4	67	21	137	9.7	32
1	76	27	142	9.7	32
1¼	86	35	151	9.7	32
1½	95	41	151	12.7	32
2	140	53	174	12.7	32
2½	162	63	190	15.7	32
3	172	78	190	19.1	32
4	206	102	219	22.4	38
5	251	128	256	28.4	38
6	279	154	256	35.1	38
8	349	203	303	41.1	38
10	432	255	370	50.8	44
12	518	303	412	60.5	44
14	575	333	442	66.5	44
16	638	381	472	76.2	44
18	702	429	504	85.9	51
20	752	478	530	95.3	51
24	899	575	603	111.3	51

CLASS 2500

NPS	A	B	C	t	W
1/2	67	16	137	9.7	32
3/4	73	21	140	9.7	32
1	83	27	145	9.7	32
1¼	102	35	161	12.7	32
1½	114	41	161	15.7	32
2	143	53	175	15.7	32
2½	165	63	201	19.1	32
3	194	78	201	22.4	32
4	232	102	232	28.4	38
5	276	128	273	35.1	38
6	314	154	273	41.1	38
8	384	198	321	53.8	38
10	473	248	390	66.5	44
12	546	289	427	79.2	44

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