FIGURE 8 BLIND DIMENSIONS BY PRESSURE CLASS
| SIZE | 150# | 300# | 600# | 900# | 1500# | 2500# | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| OD | ID | THICK | WT | OD | ID | THICK | WT | OD | ID | THICK | WT | OD | ID | THICK | WT | OD | ID | THICK | WT | OD | ID | THICK | WT | |
| 1/2" | 1.75 | 0.62 | 0.25 | 1 | 2 | 0.62 | 0.25 | 1 | 2 | 0.62 | 0.25 | 1 | 2.38 | 0.62 | 0.25 | 1 | 2.38 | 0.62 | 0.25 | 1 | 2.62 | 0.62 | 0.25 | 1 |
| 3/4" | 2.12 | 0.82 | 0.25 | 1 | 2.5 | 0.82 | 0.25 | 1 | 2.5 | 0.82 | 0.25 | 1 | 2.62 | 0.82 | 0.25 | 1 | 2.62 | 0.82 | 0.38 | 1 | 2.88 | 0.82 | 0.25 | 1 |
| 1" | 2.5 | 1.05 | 0.25 | 1 | 2.75 | 1.05 | 0.25 | 1 | 2.75 | 1.05 | 0.25 | 1 | 3 | 1.05 | 0.25 | 1 | 3 | 1.05 | 0.38 | 1 | 3.25 | 1.05 | 0.25 | 1 |
| 1-1/4" | 2.88 | 1.66 | 0.25 | 1 | 3.12 | 1.66 | 0.25 | 1 | 3.12 | 1.44 | 0.38 | 1 | 3.38 | 1.44 | 0.38 | 2 | 3.38 | 1.38 | 0.38 | 2 | 4 | 1.38 | 0.38 | 2 |
| 1-1/2" | 3.25 | 1.9 | 0.25 | 1 | 3.62 | 1.9 | 0.25 | 2 | 3.62 | 1.68 | 0.38 | 2 | 3.75 | 1.68 | 0.38 | 3 | 3.75 | 1.61 | 0.5 | 3 | 4.5 | 1.61 | 0.5 | 4 |
| 2" | 4 | 2.38 | 0.25 | 1 | 4.25 | 2.38 | 0.38 | 3 | 4.25 | 2.16 | 0.38 | 3 | 5.5 | 2.16 | 0.5 | 6 | 5.5 | 2.07 | 0.5 | 6 | 5.62 | 2.07 | 0.5 | 6 |
| 2-1/2" | 4.75 | 2.88 | 0.25 | 2 | 5 | 2.88 | 0.38 | 5 | 5 | 2.64 | 0.5 | 5 | 6.38 | 2.64 | 0.5 | 10 | 6.38 | 2.47 | 0.62 | 10 | 6.5 | 2.47 | 0.62 | 11 |
| 3" | 5.25 | 3.5 | 0.25 | 2 | 5.75 | 3.5 | 0.38 | 6 | 5.75 | 3.26 | 0.5 | 6 | 6.5 | 3.26 | 0.62 | 10 | 6.75 | 3.07 | 0.75 | 14 | 7.62 | 3.07 | 0.75 | 16 |
| 3-1/2" | 6.25 | 4 | 0.38 | 5 | 6.38 | 4 | 0.5 | 7 | 6.25 | 3.76 | 0.62 | 9 | — | — | — | |||||||||
| 4" | 6.75 | 4.5 | 0.38 | 6 | 7 | 4.5 | 0.5 | 9 | 7.5 | 4.26 | 0.62 | 13 | 8 | 4.26 | 0.75 | 18 | 8.12 | 4.03 | 0.88 | 23 | 9.12 | 4.03 | 1 | 28 |
| 5" | 7.62 | 5.56 | 0.38 | 7 | 8.38 | 5.56 | 0.62 | 15 | 9.38 | 5.3 | 0.75 | 25 | 9.62 | 5.3 | 0.88 | 31 | 9.88 | 5.05 | 1.12 | 42 | 10.88 | 5.05 | 1.25 | 51 |
| 6" | 8.62 | 6.62 | 0.5 | 12 | 9.75 | 6.62 | 0.62 | 20 | 10.38 | 6.36 | 0.88 | 34 | 11.25 | 6.36 | 1 | 47 | 11 | 6.06 | 1.38 | 63 | 12.38 | 6.06 | 1.5 | 78 |
| 8" | 10.88 | 8.62 | 0.5 | 18 | 12 | 8.62 | 0.88 | 42 | 12.5 | 8.33 | 1.12 | 61 | 14 | 8.33 | 1.38 | 99 | 13.75 | 7.98 | 1.62 | 113 | 15.12 | 7.81 | 1.75 | 129 |
| 10" | 13.25 | 10.75 | 0.62 | 33 | 14.12 | 10.75 | 1 | 63 | 15.62 | 10.42 | 1.38 | 117 | 17 | 10.42 | 1.62 | 169 | 17 | 10.02 | 2 | 213 | 18.62 | 9.75 | 2.25 | 257 |
| 12" | 16 | 12.75 | 0.75 | 58 | 16.5 | 12.75 | 1.12 | 95 | 17.88 | 12.39 | 1.62 | 175 | 19.5 | 12.39 | 1.88 | 254 | 20.38 | 11.94 | 2.38 | 365 | 21.5 | 11.37 | 2.62 | 448 |
| 14" | 17.62 | 14 | 0.75 | 71 | 19 | 14 | 1.25 | 146 | 19.25 | 13.62 | 1.75 | 216 | 20.38 | 13.62 | 2.12 | 305 | 22.62 | 13.12 | 2.62 | 496 | — | |||
| 16" | 20.12 | 16 | 0.88 | 108 | 21.12 | 16 | 1.5 | 212 | 22.12 | 15.62 | 2 | 327 | 22.5 | 15.62 | 2.38 | 407 | 25.12 | 15 | 3 | 693 | — | |||
| 18" | 21.5 | 18 | 1 | 134 | 23.38 | 18 | 1.62 | 277 | 24 | 17.62 | 2.12 | 397 | 25 | 17.62 | 2.62 | 548 | 27.62 | 16.88 | 3.38 | 934 | — | |||
| 20" | 23.75 | 20 | 1.12 | 182 | 25.62 | 20 | 1.75 | 356 | 26.75 | 19.56 | 2.5 | 584 | 27.38 | 19.56 | 2.88 | 716 | 29.62 | 18.81 | 3.75 | 1170 | — | |||
| 24" | 28.12 | 24 | 1.25 | 280 | 30.38 | 24 | 2 | 565 | 31 | 23.5 | 2.88 | 878 | 32.88 | 23.5 | 3.5 | 1254 | 35.38 | 22.62 | 4.38 | 1942 | — | |||
WHAT ARE FIGURE 8 BLINDS?
THE VERSATILE SOLUTION FOR FLOW CONTROL
Figure 8 blinds, also known as spectacle blinds or spec blinds, are specialized inline blinds that combine two functions in a single component. Named for their distinctive figure-8 shape, these devices feature both a solid plate (blind) and an open spacer ring joined together in one unit, resembling a pair of eyeglasses or spectacles when viewed from the side.
The ingenious design of Figure 8 blinds allows operators to switch between blocking flow (isolation mode) and allowing flow (spacer mode) by simply rotating the device 180 degrees. This dual-purpose functionality eliminates the need to completely remove the blind from the piping system, making it significantly faster and safer to switch between operational and maintenance states.
How Figure 8 Blinds Work:
Isolation Mode: The solid blind plate is positioned between the flanges, completely blocking flow for maintenance, repairs, or pressure testing
Flow Mode: The spacer ring is rotated into position, maintaining proper flange spacing while allowing unrestricted fluid flow through the system
Rotation Mechanism: A simple 180-degree rotation switches between modes, with the unused portion extending outside the line for easy identification
Visual Indication: The portion extending from the flange clearly shows which mode is active, providing immediate visual confirmation of system status
Figure 8 blinds are extensively used in oil and gas processing, petrochemical plants, refineries, chemical processing facilities, and power generation stations. They are particularly valuable in applications requiring frequent switching between isolation and operation, as they reduce downtime, minimize the risk of flange bolt fatigue from repeated removal and reinstallation, and enhance workplace safety by reducing the number of times workers need to break flanged connections.
FIGURE 8 BLINDS VS. TRADITIONAL PADDLE BLINDS
Understanding when to use Figure 8 blinds versus standard paddle blinds helps optimize your piping system design and operational efficiency:
CHOOSE FIGURE 8 BLINDS WHEN:
- Frequently switching between isolation and flow modes
- Quick changeovers are required to minimize downtime
- Visual confirmation of blind status is critical for safety
- Reducing flange bolt stress from repeated removal is important
- Operating in high-cycling applications
- Space allows for the extended portion outside the flange
CHOOSE PADDLE BLINDS WHEN:
- Permanent or long-term isolation is needed
- Space constraints prevent the figure-8 extension
- Lower initial cost is a priority
- Blind changes are infrequent
- Simpler inventory management is preferred
- Only isolation function is needed (no spacer required)
DUAL FUNCTIONALITY
One device serves two purposes: complete isolation with the solid blind and normal flow with the spacer ring, eliminating the need for separate components.
QUICK CHANGEOVER
Switch between isolation and flow modes in minutes with a simple 180-degree rotation, dramatically reducing downtime compared to removing and replacing separate blinds.
VISUAL STATUS INDICATOR
The portion extending outside the flange provides instant visual confirmation of whether the system is in isolation or flow mode, enhancing safety.
ASME B16.48 COMPLIANT
Manufactured to rigorous ASME standards with precision tolerances, available in multiple finishes including smooth mill and spiral serrated machine finish.
SIZING
1/2” to 24”
CLASSES
150# - 2500#
STANDARDS
ASME B16.48
SERIES
Mill or Serrated
TECHNICAL SPECIFICATIONS AND TOLERANCES
| Outside Diameter | ±0.12 inches |
|---|---|
| Inside Diameter | ±0.12 inches |
| Finish | Smooth Mill or Spiral Serrated (125-250 AARH) |
| Thickness (NPS ≤ 18) | Per B16.48 (+0.12", -0") |
| Thickness (NPS ≥ 20) | Per B16.48 (+0.19", -0") |
| Measurement Units | Inches, Pounds |