Class 8.8
One Side Bolt
ONESIDE structural blind bolts for steel joints that can only be reached from one side, like hollow columns, towers and retrofits.
About the One Side Bolt
ONESIDE bolts are structural blind bolts for steel joints you can only reach from one side, such as hollow section columns, towers, tanks and retrofits to existing steelwork. They are hot dip galvanised class 8.8 M20 assemblies with a hardened shear sleeve, step washers, a structural nut and washer and a DuraSquirt tension indicator, in seven colour-coded lengths from 65 to 165mm for grips of 12 to 20mm and 23.5 to 120mm. Choose the length by grip above; the guide below covers how the bolt works, hole sizes and Hobson's published strengths.
Also called ONESIDE bolts or one-sided structural bolts.
Features
- True structural blind (one-sided) fastening
- M30 shear capacity from an M20 bolt
- ISO property class 8.8 HR
- Hot dip galvanised
- Manual tool installation, no skilled labour
- Superior clamping strength
- Restrains vibration and movement
Applications
- High-performance hollow structural members
- Retrofitting fixtures to one-sided-access structures
- Communication and signage towers
- Tanks and pressure vessels
- Earthquake and cyclone tolerant structures
- Mining, cranes and rail gantries
What a ONESIDE bolt is
A ONESIDE bolt is a structural bolt you install and tighten from one side of the joint, for steelwork where you cannot get a spanner or a nut to the back: hollow sections, towers, tanks and existing structures. Hobson describes it as a structural blind fastening system that gives true structural strength where access is limited to one side, with superior clamping strength compared with other blind fasteners.
The bolt has a circular head that passes through the hole. A hardened split step-washer folds to go through the hole with it, then opens behind the joint so the head bears on it. A hardened sleeve over the bolt sits in the hole across the shear plane, which Hobson says gives M30 shear capacity from an M20 bolt, provided the shear plane crosses the sleeve (see choosing the length below). Hobson's joint design article says the assembly gives the full strength of property class 8.8 structural bolts to AS/NZS 4291.1 in both tension and shear, and with the sleeve, full shear strength for the hole size.
Hobson's data sheet lists the assembly as: a class 8.8 high strength bolt, a hardened split step-washer, a hardened solid step-washer, a hardened structural nut, a hardened sleeve, a spring, a DuraSquirt direct tension indicator (DTI) and a structural washer. The nut and washer are to AS 1252.
Where ONESIDE bolts are used
Hobson lists these applications:
- High performance hollow structural members.
- Retrofitting structural fixtures to hollow structures or structures with access from one side.
- Hollow communication towers and signage towers.
- Tanks and pressure vessels.
- Mining and mineral processing equipment, and road and rail gantries.
ONESIDE bolt lengths, grip ranges and colours
Every ONESIDE bolt we carry, shortest grip first. Select a row to open that bolt in the selector.
All M20 x 2.5, hot dip galvanised class 8.8. Size is thread x bolt length in mm; the selector shows bolt length x sleeve length. Sleeve, grip range, colour, thread length and minimum cavity length required (Lc,min, the clear depth needed behind the joint) in mm, from Hobson's ONESIDE data sheet 210104PR. Pack is the minimum order quantity. Tap a number to show it in the selector above.
Choosing the length and sleeve
The grip is the total thickness of steel being clamped: the fixture (plate or cleat) plus the wall of the member behind it. Pick the bolt whose grip range takes that total. Example: a 16mm plate onto a member with a 12mm wall is a 28mm grip, so the M20 x 95 x 18 (black, 23.5 to 36mm) suits.
Hobson's article says the correct sleeve length is critical: the shear plane must always cross the sleeve, so the thickness of the inner ply of the grip must be less than the sleeve length. Check that as well as the grip range.
Two things to watch, from the grip ranges: no length covers a grip between 20 and 23.5mm, and the minimum cavity behind the joint runs from 190mm for the 65mm bolt to 290mm for the 165mm bolt, so check the member is deep enough before you order.
The bolt diameter and the number of bolts come from the engineer's design; the grip only picks the length.
Hole size, pitch and edge distance
The sleeve has to pass through the joint, so the ONESIDE bolt takes a much larger hole than a standard M20 bolt. Hobson's article treats it as installed in non-standard holes: when the engineer works out the minimum edge distance and the bearing capacity of each ply, the sleeve diameter replaces the bolt diameter. The minimum pitch is the same as for a standard M20 structural bolt.
From Hobson's ONESIDE data sheet 210104PR (dimensions and components, mm). Edge distance is not a single figure: it is worked out by the engineer from the sleeve diameter and the type of edge, as Hobson's joint design article sets out. Tap a number to show it in the selector above.
| Item | Value |
|---|---|
| Hole diameter | 30 to 31mm |
| Minimum pitch (A) | 50mm |
| Minimum distance to inner edge (B) | 24mm |
| Hardened sleeve | 21mm ID, 29mm OD |
| Bolt head | 29mm diameter, 14mm thick |
| Hardened step-washers (split and solid) | 21mm ID, 42mm OD, 8.3mm thick |
| Structural washer | 21mm ID, 37.4mm OD, 4.1mm thick |
| DuraSquirt DTI | 20.7mm ID, 40.3mm OD, 3.5mm thick, 5 bumps |
| Structural nut | 31 to 32mm across flats, 20.0 to 21.3mm high |
Published bolt strengths (for the designer)
Hobson publishes the strength of one ONESIDE bolt, below. These are ultimate and proof loads of the bolt itself, not working loads and not the capacity of a joint. Joints are designed by a structural engineer to AS 4100, and Hobson's joint design article explains how:
- Bearing type joints in shear: the nominal shear capacity is the sleeve's shear capacity plus the thread's or the shank's (whichever the shear plane crosses), times the number of shear planes, then the capacity factor applies; lap connections take the reduction factor in AS 4100.
- Tension: the nominal tensile capacity comes from the data sheet or AS/NZS 4291.1 for an M20 class 8.8 bolt; combined shear and tension is checked to AS 4100.
- Ply in bearing and edge distance use the sleeve diameter in place of the bolt diameter.
- Friction type joints: the sleeve does not change the design, so tension and shear capacity are the same as a standard M20 class 8.8 structural bolt.
ONESIDE bolt M20 x 2.5, class 8.8: loads in kN from Hobson's data sheet 210104PR and joint design article 210427, which agree. Ultimate stress 830 MPa, yield 660 MPa, proof 600 MPa, hardness 23 to 34 HRC; shank stress area 314mm2, thread stress area 245mm2, core shear area 225mm2, sleeve shear area 280mm2. For use by the engineer with the capacity factors and checks above, not as working loads. Tap a number to show it in the selector above.
| Load | Ultimate (kN) | Proof (kN) |
|---|---|---|
| Tension (Ntf) | 203 | 147 |
| Shear across the shank | 162 | 117 |
| Shear across the thread | 116 | 84 |
| Shear across the sleeve | 144 | 104 |
How to install a ONESIDE bolt
Hobson says installation uses a manual tool and needs no skilled labour. The ONESIDE insert tool (20mm x 480mm) is on our bolting tools page. The steps from Hobson's data sheet:
- Put the tool onto the bolt over the install pin, pull back the tool's sleeve to engage the bolt, slide the other components back over the tool, and push the sleeve forward to lock the bolt in place.
- Fold the hardened split step-washer in the thin part of the tool, and guide the bolt and washer through the hole in the joint, drilled to the 30 to 31mm hole size.
- Rotate the tool 180 degrees to unfold the washer, then pull the tool back to press the washer against the back of the joint.
- Slide the remaining components onto the bolt and snug tighten the nut.
- Remove the installation tool and tighten the nut to the tension the design calls for, with a torque wrench or other means.
- Remove the tightening tool. The installation is complete.
Tightening and torque
Hobson gives no torque figure for the ONESIDE bolt: its sheet says to tighten the nut to the desired tension. The tension, and how it is checked, come from the engineer's specification; the assembly includes a DuraSquirt direct tension indicator washer (5 bumps on the M20).
Hot dip galvanised finish
Every ONESIDE bolt we carry is hot dip galvanised: about 50 microns of zinc, rated high corrosion resistance and recommended for long term outdoor use in Hobson's finish comparison. Hobson's corrosion guide accepts hot dip galvanising for exposed steel in the low, coastal and industrial zones; in the sea spray zone it calls for stainless steel and within 2m of a pool edge for 316 stainless, which this range does not come in. Newer galvanising can look duller than older stock; Hobson notes the brightness has no effect on performance.
ONESIDE bolts in Adelaide
Allmat supplies ONESIDE bolts, the insert tool, HBS bolts and structural bolts, nuts and washers to fabricators, steel erectors and builders across Adelaide and South Australia. Send us the bolt schedule with the grips and we will price the lot.
ONESIDE bolts for your steel connections
ONESIDE bolts, the ONESIDE insert tool, HBS bolts and structural bolts, nuts and washers are available to order from Allmat for fabricators, steel erectors, riggers, engineers and builders across Adelaide and South Australia. Order through Allmat, we pick and pack it, then click and collect from the Allmat yard or have it delivered to site.
Goes with
Questions
What is a ONESIDE bolt?
A class 8.8 M20 structural bolt assembly that is installed and tightened from one side of a steel joint. A folding step-washer opens behind the joint and a hardened sleeve sits in the hole, which Hobson says gives M30 shear capacity from an M20 bolt, provided the shear plane crosses the sleeve (inner ply thinner than the sleeve). Joint capacity is the engineer's design to AS 4100.
What hole size does a ONESIDE bolt need?
30 to 31mm, from Hobson's data sheet. The minimum pitch is 50mm and the minimum distance to the inner edge is 24mm. Edge distance is worked out by the engineer using the 29mm sleeve diameter.
What length ONESIDE bolt do I need?
Add the thicknesses being clamped and pick the bolt whose grip range covers the total: 12 to 20mm (65 x 6), 23.5 to 36mm (95 x 18), 36 to 47mm (95 x 30), 47 to 57mm (135 x 39), 57 to 73mm (135 x 48), 73 to 87mm (135 x 57) or 87 to 120mm (165 x 76). The inner ply must also be thinner than the sleeve.
What torque do I tighten a ONESIDE bolt to?
Hobson publishes no torque figure. Its sheet says to tighten the nut to the desired tension, which comes from the engineer's specification. Each assembly includes a DuraSquirt direct tension indicator.
Can I use ONESIDE bolts on SHS and RHS?
Hobson lists them for high performance hollow structural members and for retrofitting fixtures to hollow or one-side-access structures. Check the member is deep enough: the minimum cavity behind the joint is 190 to 290mm depending on the bolt length. For smaller hollow section work, see our HBS bolts.
What is the difference between ONESIDE and HBS bolts?
ONESIDE is an M20 class 8.8 assembly with a shear sleeve, folding step-washer, structural nut and DTI, installed with a manual insert tool and designed to AS 4100 using Hobson's article. HBS bolts expand a sleeve behind the wall as the bolt is tightened, from M8 to M20; they have their own page and data.
Where can I buy ONESIDE bolts in Adelaide?
Order through Allmat. Order ahead by phone on 1300 03 03 63 or send your list for a quote, then click and collect from 25 Kapara Road, Gillman, or have them delivered to site.
One Side Bolt: sizes and finishes we supply
7 lines by type and finish. Pick one above for its product code, pack sizes and dimensions.
| Type | Finish | Sizes | Lengths | Lines |
|---|---|---|---|---|
| One-side (blind) | Galvanised | M20 | 65 x 6, 95 x18, 95 x30, 135 x39, 135 x48, 135 x57, 165 x76 | 7 |
Data sheets and documents
The documents for the product you choose are listed with the selector above. Here is every One Side Bolt document from Hobson Engineering.
All One Side Bolt documents (7)
Data sheets and technical data (4)
Need them in bulk?
Add the sizes you need to your quote, or send us your list and we’ll price the lot and supply it with the rest of your order.
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