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Restrained length
Lengths are calculated with the DIPRA thrust restraint design method used in SIGMA's original Restraint Length Calculator. They apply to fittings whose restrained lengths do not overlap those of other fittings. Where they overlap, the designer evaluates the combination as a whole.
A qualified engineer should review every result before it is used in design.
Saved to this project
DIPRA, "Thrust Restraint Design for Ductile Iron Pipe," Second Edition, 1986.
Potyondy, J.G., "Skin Friction Between Various Soils and Construction Materials."
ASTM D 2487, "Classification of Soils for Engineering Purposes."
Uni-Bell PVC Pipe Association, "Handbook of PVC Pipe, Design and Construction," Dallas, Texas.
Lambe, T. William, and Whitman, Robert V., "Soil Mechanics," Series in Soil Engineering, Massachusetts Institute of Technology.
Submittals, catalogs and price lists.
One row per model. The PDF stays the document of record.
The engineer sets the pressure rating and coating in the spec. The distributor supplies the restraint with the fitting, bolts and gasket. The crew sets it at the joint.
ONE-LOK restraints at a tee.
2:1
Factor of safety on the ONE-LOK SLDE working pressure rating.
350 psi
SLDE working pressure from 3 through 16 in. It is 250 psi from 18 through 64 in.
UL · FM
SLDE is UL listed from 3 through 36 in. and FM approved from 4 through 12 in., on ductile iron pipe.
Figures from the ONE-LOK SLDE submittal. Ratings by size are in the PDF.
Questions crews ask.
Short answers. Each model page has the detail.
Both hold a joint together against thrust. A thrust block does it with poured concrete that has to cure and depends on the soil behind it. A wedge-action restraint does it at the joint: wedges grip the pipe and the gland bolts to the fitting, in the same visit.
Yes. Mechanical joint restraint, MJ restraint and restraint gland all name the same part: a gland with wedges that grip the pipe at a mechanical joint. A bell harness, sometimes called a bell restraint, adds restraint across the bell. That is SLDEH and SSLDH.
The ONE-LOK models on this page are for ductile iron pipe. PVC takes a different grip: ONE-LOK SLCE or the PV-LOK serrated clamp, on the PVC Pipe Restraints page. If you are not sure, the Selection Tool narrows it by pipe, size and pressure.
That is the restrained length, and it depends on pipe size, fitting, depth of bury, soil, trench type and test pressure. The Restraint Calculator works it out for each fitting. For example, a 12 in. ductile iron dead end tested at 150 psi, with 4 ft of cover in clay (CL) and a Type 4 trench at a 1.5 to 1 safety factor, needs 38 ft (12 m) of restrained pipe. A 90 degree horizontal bend under the same conditions needs 21 ft (6 m) on each side of the bend. Where the restrained lengths of nearby fittings overlap, the designer evaluates the joint.
Yes. D-SLDE is a domestic wedge-action gland, 3 through 48 in. Its April 2026 catalog states it is BABA and AIS compliant.
Yes. Pack numbers include the sized T-bolts and the gasket with the gland (SLDEP is the pack for SLDE). Each model page lists the pack number by size.
Have the spec in hand?
Your regional team can match it to the right model and size.
