What Size Pilot Hole For 5/16 Lag Screw

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Lag Bolts

Lag bolts are used to fasten woods to wood and metal to forest, attach objects to forest, and affix items to concrete and masonry when combined with lag expansion shields. They are heavy-duty wood screws that are available in larger sizes—both in terms of diameter and length—and usually take a hex head to facilitate college installation torque using a wrench. While lateral strength is lower than a comparable bolt and nut, lag bolts are useful when access to one side of the articulation is limited, the appearance of a nut is undesirable or through-bolt length is excessive. Lag bolts are also known as:

hex lag bolts, lag screws, omnibus screws.

Being a thread-forming-blazon screw, they create their own mating threads during installation—no nut is needed then a through-hole is not required.

Lag bolts take coarse, widely spaced threads (10 threads per inch for a one/iv" commodities, declining to just 3 1/4 threads per inch for a 1 1/four" lag bolt); threading is standard right-paw. Short lengths are fully threaded. The minimum threaded length for longer lengths is one-half the bolt length plus 1/ii", or 6", whichever is shorter. A gimlet point allows them to first threading into wood easily: "A gimlet signal is a threaded cone point usually having a point angle of 45 to 50 degrees."

Typically, lag commodities sizes range from one/iv" to 3/four" in diameter, and lengths bridge from about 1" to 16". Although 7/16" is detailed in the ASME standard, that size is not ordinarily available. Measure length from under the caput to the threaded end of the bolt.

The size of the head varies with the size of the lag bolt. Since the commodities is externally wrenched, sufficient space around the head must be allowed for wrench clearance. Table 1 lists caput width across flats, which is wrench size, and across corners, head peak and a list of threads per inch.

Steel and stainless steel are the well-nigh prevalent materials for lag bolts.

Common finishes for steel are zinc plating and hot dip galvanizing. Zinc, the most popular and to the lowest degree expensive commercial plating, offers moderate corrosion resistance. Hot dip galvanized is a thick coating of zinc that protects against corrosion in harsh environments. Stainless steel, though, is a better choice when corrosion is of business. Hot dip galvanized and stainless steel are usually recommended if the bolts (less than 1/2" in diameter) will be used with force per unit area preservative treated wood such as "ACQ" (Alkaline Copper Fourth)—check local edifice codes and contact your lumber supplier for recommendations.

Similar to wood screws, a stepped pilot hole is recommended for lag bolts. The pilot hole for the body (the unthreaded department of the shank adjacent to the head) should friction match the bolt size (3/8" hole for a iii/viii" commodities, for example). The pilot hole for the threaded section varies with bolt size and woods density, as suggested in Table 2 (see a tabular array of Species Groups for Sawn Lumber, which lists the species in each group). If the pilot hole is besides small, the bolt may break during installation. If the hole is besides large, withdrawal resistance may be compromised. Saturate drilled holes with a preservative to forestall the migration of disuse fungi if yous drill into an untreated expanse of treated lumber (consult American Forest Protection Association [AWPA] Standard M4: Standard for the Intendance of Preservative-Treated Woods Products for field treatment options). Use beeswax or paraffin to lubricate lag bolts during installation; bar soap is also popular but products that contain glycerin may accelerate bolt corrosion because glycerin is hygroscopic so it absorbs wet (be sure to remove whatever exposed lubricant residue before applying a forest finish).

Always utilise a large diameter washer under the head to distribute clamping forcefulness over a larger area and minimize pinch of the wood.

Information technology is advisable to match materials and finishes of bolts and washers (for example, use a hot dip galvanized washer with a hot dip galvanized bolt).

Ultimate tensile force of a lag bolt is said to exist developed with a thread penetration of well-nigh seven times the commodities diameter in denser species (specific gravity greater than 0.61) and 10 to 12 times the bolt bore in less dense species (specific gravity less than 0.42). (The table, Species Groups for Sawn Lumber, includes specific gravity for each of the species.)

Lag and motorcar bolts are the preferred fasteners for fastening heavy forest members in structures. A motorcar bolt with washers under the caput and nut, however, will provide increased rigidity and higher load-carrying capacity than a lag commodities.

Refer to American Society of Mechanical Engineers Standard ASME B18.2.1, Square and Hex Bolts and Screws, for specifications relating to lag bolts.

**Table 1. Lag Bolt Dimensions.** Nominal size in fractional and decimal inches, threads per inch, and head width across flats and corners and head height, in inches. (Note: Average size is calculated and rounded to nearest 64th.) ^†vii/16" is non commonly available.
Lag Commodities Dimensions
Nominal Size		Threads per Inch	Head Width		Head Height
Nominal Size			Across Flats	Across Corners	Head Height
Fraction	Decimal		Basic	Avg	Basic
1/4	0.2500	10	7/16	1/2	11/64
5/xvi	0.3125	nine	i/two	9/16	7/32
3/viii	0.3750	7	9/16	41/64	i/4
7/xvi^†	0.4375	vii	v/eight	45/64	nineteen/64
1/ii	0.5000	6	three/iv	27/32	11/32
v/8	0.6250	v	15/16	ane 1/16	27/64
three/4	0.7500	4 1/2	one ane/8	1 17/64	1/2

**Table 2. Lag Commodities Airplane pilot Hole Sizes.** Unthreaded body and threaded section airplane pilot pigsty sizes, in inches, for soft, medium and hard wood. See a table of Species Groups for Sawn Lumber for a list of species in each grouping. ^†vii/xvi" is non commonly available.
Lag Bolt Pilot Hole Sizes
Bolt Size	Pilot Hole Size
	Torso	Threaded Department
	Torso	Soft Wood Groups Three & IV	Medium Forest Group Two	Difficult Wood Grouping I
one/4	ane/4	3/32	5/32	3/xvi
5/16	v/16	9/64	iii/16	13/64
3/8	3/viii	eleven/64	xv/64	1/4
seven/16^†	7/16	thirteen/64	9/32	19/64
i/2	1/2	xv/64	v/16	11/32
5/8	5/8	v/16	thirteen/32	29/64
3/four	3/iv	13/32	ane/2	9/16