Heavy Hex Nut

Heavy hex nuts for flange bolting

These are Hobson's petrochemical heavy hex nuts, made to ASTM A194 (A194M for metric sizes). Heavy hex is the larger, thicker nut pattern used with stud bolts, and these are the nuts for the stud bolts that hold flanged pipework and plant together: Hobson pairs its ASTM A193 grade B7 studs with A194 grade 2H heavy hex nuts, and its B7 stud bolt kits come with two 2H nuts. Hobson offers the range with corrosion-resistant coatings for oil, gas and mining.

For general bolting with class 5 or 8 nuts, or stainless nuts on machine bolts and set screws, see hex nuts. Every nut here is sold individually.

A194 grades: 2H, 4L, 7, 8, 8M and more

From Hobson's petrochemical nut property sheet. Service temperatures are actual metal temperatures of the nut material and apply only to the grades the sheet lists; for the others Hobson publishes none, so check the grade against your project specification. They are not coating limits: Xylan is -40 to 205°C, and Hobson gives no temperature limit for cadmium, zinc or galvanised coatings. Select a row to open that grade.

• •2H hardness: 248 to 327 Brinell for nuts under 1-1/2 inch and 212 to 327 Brinell over 1-1/2 inch (Hobson's sheet); 24 to 35 HRC up to 1-1/2 inch and 35 HRC maximum above, on Hobson's 2H heavy hex sheet.
• •8 and 8M are the 304 and 316 stainless nuts; Hobson's B8 and B8M stud bolts are 304 and 316 stainless.

Imperial heavy hex nut sizes

Every imperial size we carry, one row per size, thread series and tapping, with the grades and finishes in each. Most nuts are UNC up to 1 inch and 8 UN (eight threads per inch) from 1-1/8 inch, the same pattern as Hobson's B7 stud bolts, but some sizes also come in UNC or UNF: match the thread to your stud. Oversize nuts are tapped larger to allow for a coated stud; the allowance is as Hobson's descriptions give it, in inches. Select a row to open exactly that size, thread and tapping. A 1/2 inch BSW grade 2H plain nut is also listed by Hobson; ask us for it.

Metric heavy hex nut sizes (ASTM A194M)

Every metric size we carry. Plain and stainless nuts are standard tapped; the hot dip galvanised 2H nuts are marked OVERSIZE in Hobson's descriptions, with no allowance stated. Select a row to open that size and tapping.

2H heavy hex nut proof loads

Hobson's 2H heavy hex sheet gives the proof load for each plain 2H nut, based on a proof stress of 175,000 psi. A proof load is a test value for the nut, not a working load for the joint: the bolting design comes from the flange or equipment specification.

Coatings: galvanised, Xylan, cadmium and plain

Coating descriptions from Hobson's petrochemical coating tables. For nuts outdoors or on exposed plant, Hobson recommends hot dip galvanised for long-term outdoor use and rates Xylan blue high for corrosion; it recommends zinc plated and zinc yellow only for indoor, low-corrosion or temporary use. Hobson gives no temperature limit for cadmium, zinc or galvanised coatings: the service temperatures in the grades table are for the nut material, not the coating, so check the coating against your bolting specification. Select a row to open that finish.

Matching nut, stud and coating

• •Grade: B7 studs take 2H nuts (Hobson sells B7 kits with two 2H nuts). Grade 8 nuts are 304 and 8M nuts 316 stainless, the materials of B8 and B8M studs.
• •Thread: check UNC, 8 UN or UNF, and imperial or metric, against the stud before ordering.
• •Tapping: oversize nuts (OVERSIZE, OS, O/S or ESSO in Hobson's descriptions, with allowances of +0.005 to +0.015 inch where given) are tapped larger for coated studs. Every Xylan blue, zinc and Xylan and Esso galvanised nut here is oversize. Plain 2H nuts in 8 UN from 1-1/8 to 2 inch come both standard and oversize (OS+0.010 or +0.015), so pick the tapping that suits your stud; ask us if unsure.
• •Tightening: Hobson's stud bolt torque guide is for lightly oiled studs clamping metal to metal, not gasketed flanges or coated studs; see the stud bolts page. Follow the flange or equipment maker's bolting procedure.

Heavy hex nuts in Adelaide

Allmat supplies ASTM A194 heavy hex nuts, B7 stud bolts and stud and nut kits to maintenance crews, pipe fitters, fabricators, mining and process plant across Adelaide and South Australia. Send us your list with sizes, grades, coatings and tapping and we will price the lot.

Questions