Lag & Carriage Bolts

Carriage Bolts come with a round head and aCarriage Bolt - Haydon Bolts Inc square neck, are commonly used in wood connections. The square neck under the round head allows the bolt to set into the hole in the wood to prevent the head from turning. Carriage Bolts are generally manufactured to the A307 Grade A specification, in domestic or import. 

Finishes: Plain (black) & Galvanized

Grades: A307 A, A449, A588

Carriage Bolts Standard Thread Length Formulas

Bolt lengths  6″: Thread length = (2 X diameter) + 1/4″
Bolt lengths > 6″: Thread length = (2 X diameter) + 1/2″

Carriage Bolt Dimensions

Bolt DiameterBody Diameter (E)Head Diameter (A)Head Height (H)Square Width (O)Square Depth (P)Corner Radious on Square (Q)Fillet Radius (R)
MaxMinMaxMinMaxMinMaxMinMaxMinMaxMax
No. 100.1990.1590.4690.4360.1140.0940.1990.1850.1250.0940.0310.031
1/4"-0.19000.260.2130.5940.5630.1450.1250.260.2450.1560.1250.0310.031
5/16"-0.25000.3240.2720.7190.6881.1760.1560.3240.3070.1870.1560.0310.031
3/8"-0.37500.3880.3290.8440.7820.2080.1880.3880.3680.2190.1880.0470.031
7/16"-0.43750.4520.3880.9690.9070.2390.2190.4520.4310.250.2190.0470.031
1/2"-0.5000.05150.4441.0941.0320.270.250.5150.4920.2810.250.0470.031
5/8"-0.62500.6420.5591.3441.2190.3440.3130.6420.6160.3440.3130.0780.062
3/4"-0.75000.7680.6781.5941.4690.4060.3750.7680.7410.4060.3750.0780.062
7/8"-0.87500.8950.7951.8441.7190.4590.4380.8950.8950.4690.4380.0940.062
1"-1.00001.0220.912.0941.9690.5310.51.0220.990.5310.50.0940.062
ASME B18.5 2008 - Table 2 Dimensions of Round Head Square Neck Bolts


Lag Bolts are directly screwed into wood. They have a hex head and a cylindrical shaft with smooth and externally threaded parts along its length. The thread tapers to a sharp point at its end to help engage the screw by embedding into the surface of the wood. On installation the Lag Bolt passes through two pieces of wood being connected, the first piece of wood has a pilot hole that allows the bolt to freely pass through, while the threads engage into the second piece of wood. Domestic or import are available. 

Diameter: 3/8″ through 1″Lag Bolt Dimension Drawing - Haydon Bolts Inc

Grades: A307-Grade A, A153-C, 18-8 Stainless Steel

Finishes: Plain (black) Hot Dip Galvanized, Zinc Plated

Lag Bolts Standard Thread Length Formulas

The minimum thread length shall be equal to 1/2 of the nominal screw length plus a half inch or 6″ which ever is shorter. Screws too short for the formula thread length shall be threaded as close to the head or shoulder as practicable.

Pilot Hole Diameter for Lag Bolts

Bolt DiaShank (Unthreaded)Pilot Hole Dia
3/83/815/64
7/167/169/32
1/21/25/16
9/169/1623/64
5/85/813/32
3/43/41/2
7/87/839/64
1123/32
11/811/853/64
11/411/415/16

Hex Lag Screws Dimensions

Bolt DiameterBody/Shoulder Diameter (E)Width Across the Flats (F)Width Across Corners (G)Head Height (H)Shoulder Length (S)Radius of Fillet (R)
MaxMinBasicMaxMinMaxMinBasicMaxMinMinMaxMin
No. 100.1990.1789/320.2810.2710.3230.3091/80.140.110.0940.030.01
1/40.260.2377/160.4380.4250.5050.48411/640.1880.150.0940.030.01
5/160.3240.2981/20.50.4840.5770.5527/320.2350.1950.1250.030.01
3/80.3880.369/160.5620.5440.650.621/40.2680.2260.1250.030.01
7/160.4250.4215/80.6250.6030.7220.68719/640.3160.2720.1560.030.01
1/20.5150.4823/40.750.7250.8660.82611/320.3640.3020.1560.030.01
5/80.6420.60515/160.9380.9061.0831.03327/640.4440.3780.3120.060.02
3/40.7680.7291-1/81.1251.0881.2991.241/20.5240.4550.3750.060.02
7/80.8950.8521-5/161.3121.2691.5161.44737/640.6040.5310.3750.060.02
11.0220.9761-1/21.51.451.7321.65343/640.70.5910.6250.090.03
1-1/81.1491.0981-11/161.6881.6311.9491.8593/40.780.6580.6250.090.03
1-1/21.2771.2231-7/81.8751.8122.1652.06627/320.8760.7490.6250.090.03
ASTM B18.2.1 2015 Table 15 - Dimensions of Hex Lag Screws

The above tables should be used as a guide only, consult your project engineer for exact measurements.

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