The mismatch that stops every project cold
The concrete is poured. The anchor bolts are set. The new pole arrives on site. The base plate does not fit the bolts. The job is dead until someone finds a fix. This happens on light pole projects more often than anyone in the industry wants to admit, and it almost always traces back to the same root cause: someone confused bolt circle with bolt square. A 10" bolt circle and a 10" bolt square are not the same pattern. They are off by 3 inches. That 3 inches is the difference between a pole that drops onto the bolts in 5 minutes and a change order that costs thousands of dollars and weeks of delay.
This guide covers everything a contractor needs to know about light pole anchor bolts: how to measure them, how to order them, and how to fix them when they do not match.
Bolt circle vs. bolt square: the measurement that causes most field problems
A standard light pole base has four anchor bolts arranged in a square pattern. There are two ways to measure this pattern, and mixing them up is the single most common cause of base plate mismatches.
Bolt circle
The diagonal measurement. Measure from the center of one bolt to the center of the bolt diagonally opposite. This is the diameter of a circle that passes through the centers of all four bolts. Bolt circle is the industry standard measurement. When a pole manufacturer specifies a bolt pattern, they are almost always specifying bolt circle.
Bolt square
The side measurement. Measure from the center of one bolt to the center of the adjacent bolt (not the diagonal). This is the length of one side of the square formed by the four bolts. Bolt square is always a smaller number than bolt circle for the same physical pattern.
Bolt Square / 0.707 = Bolt Circle
Bolt Circle to Bolt Square:
Bolt Circle x 0.707 = Bolt Square
Example:
A field measurement of 7.07" bolt square:
7.07 / 0.707 = 10.0" bolt circle
A spec sheet says 10" bolt circle:
10.0 x 0.707 = 7.07" bolt square
The critical rule: always confirm which measurement you are using. When you call a supplier and say "I need a pole with a 10-inch bolt pattern," and the supplier hears "10-inch bolt circle" but you meant "10-inch bolt square," the pole that arrives will have a bolt circle of 10 inches (bolt square 7.07 inches) and it will not fit your bolts that are set at a 10-inch bolt square (bolt circle 14.14 inches). That is a 4-inch mismatch in every direction. Always say "10-inch bolt circle" or "10-inch bolt square." Never just "10-inch bolt pattern."
Common anchor bolt sizes for light poles
| Pole height | Typical bolt diameter | Typical bolt circle | Typical bolt count | Notes |
|---|---|---|---|---|
| 10-15 ft | 3/4" | 8.5-10" | 4 | Decorative, pedestrian-scale poles. Lightweight fixtures only. |
| 15-20 ft | 3/4" | 8.5-11" | 4 | Standard commercial parking lot poles. Most common size range. |
| 20-30 ft | 1" | 10-13" | 4 | Taller parking lot and roadway poles. Bolt circle increases with height and wind load. |
| 30-40 ft | 1" to 1-1/4" | 13-17" | 4-6 | Large area and highway poles. Some manufacturers use 6 or 8 bolt patterns at this height. |
| 40+ ft | 1-1/4" to 1-1/2" | 17-25" | 6-8 | High-mast poles. Always verify with the pole manufacturer's specification. |
These are general ranges, not specifications. The exact bolt diameter, bolt circle, bolt length, and projection are determined by the pole manufacturer based on the specific pole model, wall thickness, height, wind speed rating, and fixture EPA loading. Always use the bolt dimensions from the pole manufacturer's specification, not from a generic table. The anchor bolt set should ship with a steel template that matches the pole base. Use it.
ASTM F1554: the specification that governs light pole anchor bolts
ASTM F1554 is the standard specification for steel anchor bolts used to anchor structural supports to concrete foundations. It is the governing specification for virtually all light pole anchor bolts in the United States. F1554 defines three grades based on minimum yield strength:
| Grade | Min. yield strength | Color code | Material | Typical use in lighting |
|---|---|---|---|---|
| Grade 36 | 36 ksi | Blue | Low carbon steel (A36) | Light-duty applications. Always weldable. Grade 55 may be substituted at supplier's option. |
| Grade 55 | 55 ksi | Yellow | Modified mild steel | The most commonly specified grade for lighting and traffic signal poles. Higher strength than Grade 36 with good ductility. |
| Grade 105 | 105 ksi | Red | Heat-treated medium carbon alloy | High-mast and heavy-duty poles. Highest strength grade. Can be hot-dip galvanized without affecting mechanical properties. |
Source: ASTM F1554-20, Standard Specification for Anchor Bolts, Steel, 36, 55, and 105-ksi Yield Strength. Color coding (Blue/Yellow/Red) is specified per F1554 Section 11 for field identification.
All light pole anchor bolts should be hot-dip galvanized per ASTM F2329. They are permanently exposed to weather. Zinc plating is not acceptable for this application; it does not provide sufficient corrosion protection for the decades-long service life expected of a pole foundation.
Anchor bolt configurations: L-bolt vs. straight rod
Light pole anchor bolts come in two primary configurations:
L-bolt (bent anchor bolt): A straight rod with a 90-degree bend (hook) at the bottom end. The hook resists pullout from the concrete through mechanical bearing. L-bolts are the most common configuration for light poles because they are simple to install during initial construction. The hook end is embedded in the concrete before it cures. Typical hook length is 3-4 inches for 3/4" bolts and 4-6 inches for 1" bolts.
Straight rod (all-thread or headed): A straight rod that is either threaded on both ends or fully threaded, sometimes with a hex head or plate washer at the embedded end. Straight rods are common in retrofit applications where epoxy-set anchors are drilled into existing concrete foundations. They are also used in new construction when the engineer specifies higher pullout resistance than an L-bolt provides.
Thread specification: Light pole anchor bolts use UNC (Unified National Coarse) threads. The threaded projection above the concrete must be long enough to accommodate the leveling nut, the base plate, the top nut, and 1-2 threads of projection above the top nut. Typical thread length is 6 inches (minimum) on the exposed end. The pole manufacturer's specification will call out the required projection above the finished concrete grade, typically 3-5 inches.
The pre-pour checklist: how to prevent the mismatch
Every anchor bolt mismatch traces back to a failure in one of these steps. Check them all before the concrete truck arrives.
| Step | Action | What goes wrong if you skip it |
|---|---|---|
| 1 | Confirm the pole model number and verify the anchor bolt specification from the pole manufacturer's data sheet. Get the bolt circle, bolt diameter, bolt length, and projection. | Assumptions based on "the same pole we used last time" result in wrong-size bolts when the manufacturer updated the base plate design. |
| 2 | Verify the template matches the pole. Compare the bolt circle on the steel template to the bolt circle on the pole manufacturer's spec sheet. They must be identical. | Wrong template ships with the bolts. This happens often enough that multiple manufacturers specifically warn about it in their installation guides. |
| 3 | Confirm bolt circle vs. bolt square in every communication. When relaying measurements to the concrete crew, always say "bolt circle" or "bolt square" explicitly. | Field crew interprets "10-inch pattern" as bolt square, sets bolts at 10" side-to-side, pole arrives expecting 10" bolt circle. 3-inch mismatch. |
| 4 | Set the template level and plumb. Verify the template is level in both axes and that the wiring access opening is oriented correctly (toward the electrical feed direction). | Tilted bolts make it impossible to slide the base plate over them. Rotated template puts the wiring hole away from the conduit. |
| 5 | Verify projection after the pour. Measure the bolt projection above the finished concrete grade against the pole manufacturer's specification. Check immediately, before the concrete cures. | Bolts set too deep cannot be raised. Not enough projection means the nut cannot engage sufficient threads to develop the required clamping force. |
When the bolts do not match: three fixes
It happened. The pole is on site and the base plate does not fit the bolts. Here are the options, from least to most disruptive:
1. Anchor bolt adapter blocks. Threaded steel blocks that screw onto the existing anchor bolts (in place of the leveling nut) and provide a new stud at a different bolt circle. Available for 3/4" and 1" bolts. They can adjust the bolt circle by up to 2.2-5 inches depending on the model and can correct both bolt circle errors and clocking (rotation) errors. This is the fastest fix: no concrete work, no drilling, no re-engineering the foundation. Verify the adapter is rated for the pole height and wind load.
2. Epoxy-set anchor bolts. Drill new holes in the existing foundation, set new straight-rod anchor bolts using a structural epoxy system (such as Hilti HIT-RE 500 V4 or equivalent), and cut the old bolts below grade. This requires a structural engineer to verify the existing foundation can support the new bolt locations and the epoxy pullout capacity meets the pole's base reactions. Allow the epoxy to cure fully before loading.
3. Break out and re-pour. Remove the existing foundation, set new anchor bolts with the correct template, and pour new concrete. This is the most expensive and time-consuming fix, but it is sometimes the only option when the existing foundation is too small, too shallow, or too deteriorated to support adapter blocks or epoxy anchors.
Do not field-modify the pole base plate. Drilling new holes in the base plate or slotting existing holes to fit mismatched bolts compromises the structural integrity of the pole. This creates a safety liability. If the base plate does not fit the bolts, fix the bolt side (adapters, epoxy, or new foundation). Do not modify the pole.
Frequently asked questions
What is the difference between bolt circle and bolt square?
Bolt circle is the diagonal measurement across a 4-bolt pattern (center to center of opposite bolts). Bolt square is the side measurement (center to center of adjacent bolts). Bolt circle is always larger. To convert bolt square to bolt circle, divide by 0.707. Bolt circle is the industry standard. Always specify which measurement you are referencing.
What size anchor bolts do light poles use?
Most commercial light poles (15-25 ft) use 3/4" or 1" diameter bolts in a 4-bolt pattern with bolt circles ranging from 8.5" to 13". Taller poles (30+ ft) may use 1-1/4" or larger bolts with wider bolt circles and 6-8 bolt patterns. The exact specification comes from the pole manufacturer, not from a generic table. Always verify against the pole's data sheet.
What ASTM specification covers light pole anchor bolts?
ASTM F1554. Three grades: 36 (blue, 36 ksi yield), 55 (yellow, 55 ksi yield, most common for lighting), and 105 (red, 105 ksi yield). All should be hot-dip galvanized per ASTM F2329. Grade 55 is the standard for lighting and traffic signal poles.
What do I do if the anchor bolts do not match the pole?
Three options from least to most disruptive: (1) Anchor bolt adapter blocks that thread onto existing bolts and provide new studs at the correct bolt circle. (2) Epoxy-set new anchor bolts drilled into the existing foundation. (3) Break out and re-pour the foundation. Never modify the pole base plate. See the detailed fix guide above.
