Through Bolt Anchor

What a through bolt is

A through bolt (Mungo throughbolt) is a torque-controlled expansion anchor for concrete, the same family as a wedge anchor: a threaded bolt with an expansion sleeve at the tip, a washer and a nut. You drill through the fixture into the concrete, drive the anchor through, and tighten the nut to the installation torque. That draws the tapered end of the bolt up into the expansion sleeve, which presses out against the side of the hole. The M2-I and M2R-I versions have an internal thread instead of the external thread and nut, for a bolt or rod to screw into.

Fixing steel base plates, brackets and timber bottom plates to concrete slabs is a common use. For any structural or safety-critical fixing, the range, size, embedment, edge distance and spacing come from the engineer's or designer's specification, using the ETA or data sheet values for that range. Every Hobson document for these anchors covers concrete only (strength classes C20/25 to C50/60); for brick or block, use a chemical anchor with a mesh sleeve, following that anchor's data sheet for masonry.

Which through bolt? M1T, M1TR, M2, M2R or M2F

• •M1T (zinc plated) and M1TR (316 stainless): European Technical Assessment (ETA-12/0547 and ETA-12/0375) Option 1, for cracked and non-cracked concrete. Seismic category C1 for M8 to M16, and C2 for M10, M12 and M16 (the ETAs give no complete C2 values for M8). Both ETAs include fire resistance values; Hobson's data sheets list F120.
• •M2 (zinc plated): Hobson's M2 data sheet lists ETA Option 7 for non-cracked concrete only, and no fire resistance performance assessed. The data sheet gives its M6 to M16 codes Mungo's GreenTec zinc-nickel alloy layer; we make no GreenTec claim for the two M20 codes (M20 x 130/10 and M20 x 160/30).
• •M2R (316 stainless): ETA-05/0199 Option 7, non-cracked concrete only, static and quasi-static loads, no fire resistance performance assessed. The ETA covers anchors from 65mm (M6), 80mm (M8), 95mm (M10), 110mm (M12) and 130mm (M16) long, so our shorter M2R codes are outside it.
• •M2F (hot dip galvanised): Hobson's documents for the M2F include no data sheet, ETA or installation data. Hobson publishes no rating for it, so for structural or safety fixings use an ETA range or an anchor the engineer or designer specifies.
• •Older M1T codes listed by length only (for example M20 x 165 and M24 x 190): these stock codes are not in the M1T data sheet or ETA-12/0547, even where the length matches an approved code, and the M20 and M24 sizes are not in the ETA at all. For an approved anchor choose one of the length / fixture thickness codes (for example M12 x 200/100). No approval or installation data is published for the older codes, so do not specify them where an approval is needed.

Through bolt sizes and approvals

The two numbers in a length such as 120/20 are the anchor length and the maximum fixture thickness, both in mm: an M12 x 120/20 fixes through up to 20mm of plate, packers and grout. Choose a length whose second number is at least your fixture thickness. Select a row to open that range and size in the selector.

Through bolt drill size, hole depth and torque

Each range has its own installation values, from its own ETA or data sheet. The drill size is the thread size. Drill by hammer drilling only, clean the dust out of the hole, and tighten with a calibrated torque wrench to the installation torque. Mungo's data sheets say an anchor may only be set once.

Edge distance, spacing and concrete thickness

The approvals apply only when each anchor is far enough from the edge of the slab, far enough from the next anchor, and in concrete thick enough. The minimum edge distance only applies with at least the spacing shown beside it, and the minimum spacing only with at least the edge distance beside it. Mungo's M1T data sheet says loads must be reduced at the minimum spacing, edge distance and member thickness, and that the data must be checked by an engineer experienced in anchorage and concrete work. Timber bottom plates and post bases often sit close to a slab edge, so check positions against this table before you drill.

If a hole is aborted, the ETAs call for a new hole at least twice the depth of the aborted hole away, or closer only if the aborted hole is filled with high strength mortar and is not in the direction of a shear or oblique tension load.

Which through bolt for outdoors?

• •M1T zinc plated: ETA-12/0547 limits it to structures in dry internal conditions. Use it inside, not where it is exposed to the weather or damp.
• •M1TR and M2R 316 stainless: their ETAs allow dry internal conditions, external atmospheric exposure including industrial and marine environments, and permanently damp internal conditions, provided there are no particularly aggressive conditions. ETA-12/0375 gives examples of those: permanent or alternating immersion in seawater, the seawater splash zone, the chloride atmosphere of indoor swimming pools, and extreme chemical pollution.
• •M2 zinc plated: Hobson's documents give no outdoor use conditions. Hobson's finish comparison rates zinc plating low corrosion resistance, for indoor and non-corrosive environments (GreenTec on the M6 to M16 is a coating, not a use condition).
• •M2F hot dip galvanised: Hobson rates hot dip galvanising high corrosion resistance for long term outdoor use, and its corrosion guide lists hot dip galvanising or stainless for exposed fixings in low, coastal and industrial zones (stainless in seaspray zones and within 2m of a pool). It has no ETA or installation data, as above.

Through bolt, sleeve anchor, concrete screw or chemical anchor?

• •Through bolt: through-fixed in solid concrete and loaded once tightened; the M1T and M1TR carry ETA Option 1 for cracked concrete.
• •Sleeve anchor: also through-fixed in solid concrete, with more head styles.
• •Concrete screw: screws straight into a drilled hole in concrete; its own data sheet gives its installation values, edge distances and spacing.
• •Chemical anchor: a stud set in resin. In brick and hollow block, chemical anchors are set through a sleeve (our chemical anchor sleeves are compared on the chemical anchor page); follow that anchor's data sheet for masonry. Internal thread anchors set in resin are on the same page.

Through bolts in Adelaide

Allmat supplies Mungo through bolts, wedge anchors, concrete screws, chemical anchors and SDS drill bits to builders, steel fabricators, electricians, plumbers and trade across Adelaide and South Australia. Add them to a quote with the rest of your list and we will price the lot.

Questions