What Size Pilot Hole For 1/4 Lag Screw

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Lag Bolts

Lag bolts are used to spike wood to woods and metallic to wood, attach objects to wood, and braze items to physical and masonry when combined with lag expansion shields. They are heavy-duty forest screws that are available in larger sizes—both in terms of bore and length—and usually take a hex head to facilitate higher installation torque using a wrench. While lateral force is lower than a comparable commodities and nut, lag bolts are useful when access to 1 side of the joint 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, coach screws.

Being a thread-forming-type screw, they create their ain mating threads during installation—no nut is needed so a through-hole is non required.

Lag bolts have coarse, widely spaced threads (ten threads per inch for a 1/four" bolt, failing to merely 3 1/4 threads per inch for a 1 one/4" lag bolt); threading is standard correct-hand. 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 start threading into wood easily: "A gimlet bespeak is a threaded cone point usually having a point bending of 45 to l degrees."

Typically, lag bolt sizes range from i/4" to 3/four" in diameter, and lengths span from about 1" to 16". Although 7/16" is detailed in the ASME standard, that size is not commonly available. Measure length from under the head to the threaded end of the bolt.

The size of the head varies with the size of the lag bolt. Since the bolt is externally wrenched, sufficient space around the head must exist immune for wrench clearance. Table 1 lists caput width beyond flats, which is wrench size, and beyond corners, caput height and a listing of threads per inch.

Steel and stainless steel are the virtually prevalent materials for lag bolts.

Mutual finishes for steel are zinc plating and hot dip galvanizing. Zinc, the almost popular and least 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 meliorate choice when corrosion is of business organisation. Hot dip galvanized and stainless steel are ordinarily recommended if the bolts (less than 1/ii" in diameter) will be used with pressure preservative treated wood such as "ACQ" (Alkali metal Copper 4th)—check local building codes and contact your lumber supplier for recommendations.

Similar to woods screws, a stepped pilot hole is recommended for lag bolts. The pilot pigsty for the body (the unthreaded section of the shank adjacent to the head) should match the bolt size (three/8" hole for a 3/8" bolt, for example). The pilot hole for the threaded section varies with bolt size and wood density, as suggested in Table 2 (see a table of Species Groups for Sawn Lumber, which lists the species in each group). If the airplane pilot hole is too small, the bolt may break during installation. If the hole is too big, withdrawal resistance may be compromised. Saturate drilled holes with a preservative to forestall the migration of decay fungi if you drill into an untreated area of treated lumber (consult American Wood Protection Association [AWPA] Standard M4: Standard for the Care of Preservative-Treated Woods Products for field treatment options). Employ beeswax or paraffin to lubricate lag bolts during installation; bar lather is besides popular simply products that incorporate glycerin may accelerate bolt corrosion considering glycerin is hygroscopic so it absorbs moisture (exist certain to remove any exposed lubricant residue before applying a wood stop).

Always use a big bore washer under the head to distribute clamping force over a larger area and minimize compression of the wood.

It is advisable to lucifer materials and finishes of bolts and washers (for example, utilise a hot dip galvanized washer with a hot dip galvanized commodities).

Ultimate tensile strength of a lag bolt is said to be adult with a thread penetration of about 7 times the commodities diameter in denser species (specific gravity greater than 0.61) and 10 to 12 times the bolt diameter 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 wood members in structures. A machine bolt with washers under the head and nut, all the same, will provide increased rigidity and college load-carrying capacity than a lag commodities.

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

**Tabular array 1. Lag Bolt Dimensions.** Nominal size in fractional and decimal inches, threads per inch, and head width across flats and corners and head pinnacle, in inches. (Annotation: Average size is calculated and rounded to nearest 64th.) ^†7/sixteen" is not normally available.
Lag Commodities Dimensions
Nominal Size		Threads per Inch	Head Width		Head Peak
Nominal Size			Across Flats	Beyond Corners	Head Peak
Fraction	Decimal		Basic	Avg	Basic
i/4	0.2500	10	7/16	1/2	11/64
5/16	0.3125	9	i/2	nine/16	seven/32
3/viii	0.3750	7	nine/16	41/64	1/four
7/16^†	0.4375	vii	5/8	45/64	19/64
one/two	0.5000	half dozen	iii/four	27/32	11/32
5/viii	0.6250	5	xv/16	i 1/16	27/64
3/4	0.7500	4 1/2	1 1/eight	i 17/64	1/two

**Tabular array 2. Lag Bolt Pilot Hole Sizes.** Unthreaded body and threaded department pilot hole sizes, in inches, for soft, medium and hard wood. See a table of Species Groups for Sawn Lumber for a listing of species in each group. ^†7/16" is not commonly bachelor.
Lag Bolt Pilot Hole Sizes
Bolt Size	Pilot Pigsty Size
	Trunk	Threaded Section
	Trunk	Soft Wood Groups Iii & Iv	Medium Wood Group Two	Difficult Wood Grouping I
1/four	1/4	3/32	5/32	3/sixteen
5/xvi	v/sixteen	9/64	3/sixteen	13/64
3/8	three/eight	11/64	15/64	1/4
7/16^†	vii/xvi	13/64	9/32	nineteen/64
ane/ii	1/2	15/64	5/xvi	11/32
five/8	five/viii	5/16	13/32	29/64
iii/4	iii/4	13/32	i/2	9/16

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