Z-LOK Metallic Piston Rings

April 21, 2020

Zatkoff Seals & Packings Z-LOK piston rings from Grover Corporation excel in a diverse range of demanding applications. The Z-LOK joint design provides superior sealing efficiency by tightly controlling the leak pattern and enhancing seal stability.

Benefits of the Z-LOK Metallic piston ring include:

  • Bi-directional
  • Requires fewer rings than traditional designs
  • Passes over ports without port-clipping
  • Compensates for ring and cylinder wear
  • Compatible with pressures up to 5,000 psi
  • Maintains oil bypass at or below acceptable levels in most applications

Piston rings are typically manufactured of cast iron, adhering to SAE J929 specifications. The cast iron is alloyed to provide the best combination of impact strength, temperature stability, and wear characteristics for most standard hydraulic applications. Alternative materials like nodular iron, bronze alloys, and stainless steel can also be used to solve complex or unique sealing applications.

As the standard protective coating per SAE AMS2481, manganese phosphate is applied to the surface of ferrous Z-LOK piston rings. Platings are also available that are designed to improve lubrication and enhance wear resistance.

Designing an application with three Z-LOK piston rings ensures long-term sealing performance. Foreign particles that are often present in a cylinder accumulate in outboard grooves and negatively impact the outer side face seal surfaces — but with the three-ring design, these particles remain trapped in the outboard grooves, allowing the center ring to function normally.

Z-LOK Installation Data


Outside diameter of all piston rings are machined to conform to the minimum bore diameter.


Piston rings are supplied to the following standard widths and tolerances, unless otherwise specified.

Nominal Width Actual Width Width Tolerance
3/32 .0935 Ring O.D. Tolerance
1/8 .1240 .500 – 5.970 +.000 – .001
5/32 .1550
3/16 .1865
1/4 .2490 5.971 – 9.970 +.000 – .0015
5/16 .3110
3/8 .3730
7/16 .4360 9.971 – 19.970 +.000 – .002
1/2 .4980
5/8 .6230
3/4 .7470 19.971 – 30.500 +.000 – .0025
7/8 .8720
1 .9970

Groove Design Data

Groove recommendations conform to ANSIB93.36 and NFPA Std. Tc.19.11.

Groove Width

For nonstandard rings to slide freely within the groove, their grooves must be at least .001” wider than the maximum piston ring width.

Radial Wall

All non-standard piston rings are bored to the dimensions and tolerances of a comparable standard diameter ring, unless otherwise specified.

End Clearance

End clearance depends on the design, material, and application of the ring.

Diameter Butt & Angle Cut End Clearance Z-LOK & Step Cut End Clearance
.500 – 4.561 .003/.010 .005/.015
4.562 – 19.970 .005/.015 .010/.020
19.971 – 30.500 .010/.025 .015/.030

Groove Depth

For nonstandard rings to bottom in the groove when compressed to its working diameter, grooves should be at least .015” deeper than the maximum radial wall dimensions of the piston ring.


Wall finish isn’t necessary when using metallic piston rings — satisfactory results have been found in bores ranging from 4 to 80 RMS. However, excellent ring seating occurs in cylinders with wall finishes from 16 to 40 RMS.

Download Z-LOK Brochure

For more information about our selection of Z-LOK metallic piston rings, contact your local Zatkoff representative. We also provide alternate joint diameters, widths, radial walls, and end clearances to meet specific design requirements.


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