A bolt pattern is one of the few specifications that a fleet cannot negotiate after the fact. Either the holes line up or the blade does not mount, and with a segmented flexible blade the pattern is repeated at every segment joint, so a small error is multiplied across the assembly. Measuring the pattern from the blade in service is the step that prevents it.

Which JOMA Blade Bolt Pattern Points Decide Fitment

Hole diameter, spacing and row position decide fitment.

Four dimensions matter: the diameter of each hole, the centre-to-centre spacing between holes in a row, the distance from the top edge of the blade to the first row, and the number of rows. A pattern is defined by all four, not by a nominal name.

Fleets often refer to a pattern by the equipment make, and that reference is only as good as the assumption behind it. A make may use more than one pattern across model years, and a machine that has been through previous replacements may no longer carry its original mounting hardware. Measuring the blade in service removes both uncertainties, and the procedure is set out in the guide to measuring a blade for replacement.

With segmented blades there is a second consideration: the pattern has to be consistent across the full blade, because each segment is located by its own holes. Where the mounting face has worn unevenly, the effective pattern varies along the blade, and individual segments can end up seated differently. Checking the face at the same time as the pattern is what catches that before the segments are ordered.

How Hole Diameter, Spacing and Rows Interact

Each dimension fails differently in practice.

Hole diameter decides whether the fastener seats and clamps, spacing decides whether the segment is pulled into position, and row position decides where the working face sits relative to the moldboard. A pattern can be right in one of these and wrong in another.

A hole diameter that is too small prevents the fastener from seating and forces the workshop to dress the hole, which reduces the clamping area. A diameter that is too large allows movement under load, which loosens the segment and accelerates wear at the joints. Spacing errors are less obvious at fitting and more damaging in service: where the centre-to-centre distance is slightly wrong, the fasteners pull the segment into line and distort the flexible section, so the symptom appears as uneven clearing rather than as a loose blade.

Row position interacts with both. The distance from the top edge to the first hole row determines how the segment sits relative to the moldboard and therefore at what height the working face meets the surface. A pattern with the correct spacing but the wrong row position will mount and will not sit as intended, and on a blade specified for a particular surface condition, that difference matters.

Grade, Geometry and Material Choices Around Mounting

Mounting requirements constrain what can be specified elsewhere. A pattern with fewer fixing positions concentrates load at each one, which raises the demand on the segment’s structure and on the fasteners. A pattern with more positions distributes load but increases the number of points that must be torqued correctly and re-checked through the season.

Grade selection is unaffected by the pattern, but the assembly mass is not. SENTHAI engineers the hardness and toughness balance against stated service conditions using hardness on the HRA scale together with carbide grain size, and supplies micro grain inserts in trapezoid and bullnose shapes, which allows grade and geometry to be specified with the mounting arrangement rather than separately from it. A heavier arrangement carries more load into the same number of fixing positions, which is a design consideration rather than a procurement one.

Production control is what makes a pattern reproducible. SENTHAI manufactures in Rayong, Thailand, in a US-invested plant using non-China raw materials, with the full chain in-house from wet grinding and robotic pressing at up to 500 tons through vacuum and low-pressure sintering, automated high-temperature induction brazing and finishing, holding plus or minus 0.02 mm dimensional tolerances on carbide components. Where the pattern is produced in the same facility as the drawing, a follow-on order reproduces the fitment rather than approximating it.

Fitment and Tolerance Requirements Across Makes

AASHTO and DIN patterns are the common conventions, and SENTHAI validates fitment against them before release, with AASHTO published standards as the reference for agency specifications and DIN covering European and export conventions. Where an OEM mounting interface is involved, the equipment documentation is the authority and SAE standards for mobile machinery describe the interfaces those designs were built around.

Three checks prevent most cross-make problems. Confirm hole diameter, because nominally identical patterns vary between manufacturers. Confirm the row count and position, since a two-row blade is not interchangeable with a single-row one even where the outer dimensions agree. And confirm the installed length, because the same pattern can be used on blades of different widths, which changes the segment arrangement required.

Where a fleet runs several makes, treating each as a separate requirement is what keeps the specification enforceable. A single pattern statement covering an order that contains several configurations is not a fitment validation, and it creates ambiguity about which configuration was accepted when a delivery is checked.

A practical habit makes the checks easier to repeat. Keep a pattern record for each plow group containing the four measured dimensions, the date the reading was taken, the condition of the mounting face at the time and the hardware set in use. When a blade is replaced or a machine is repaired, the record shows whether the pattern has changed, which is otherwise only discovered when a new segment does not fit.

That record also answers a question that arises whenever equipment is added or replaced. A plow acquired second-hand may share a make and model with existing units and still carry a different pattern, particularly if it has been modified. Checking the new unit against the pattern record on arrival takes minutes and prevents it from becoming the one truck in the fleet that cannot use stock from the rack.

Evidence to Request With a JOMA Blade Quote

Pattern evidence is straightforward to request. Ask for written confirmation that the segments match the pattern dimensions supplied, the dimensional inspection results at the mounting holes, and the hardware set required including bolt length and torque value. SENTHAI inspects and archives every batch, and the quality control and traceability page describes what that record contains.

Two further items complete the package. Grade data referenced to a test method such as those published by ASTM, and a statement of the pattern standard the segments are produced to. Where a fleet is publicly funded, supplier registration for federal awards is handled through SAM.gov, and general procurement guidance is published by GSA. Noting those requirements early lets bidders plan rather than discover them after award.

A cross-fleet treatment of the same subject, covering how bolt hole patterns are standardised across mixed equipment, is set out in the guide to verifying plow blade bolt hole patterns.

Common Bolt Pattern Errors and Their Cost on JOMA Blade Bolt Patterns

The most common error is ordering from a make and model reference. Catalogue patterns describe nominal equipment, and the machine in service may differ because of previous replacements, repairs, aftermarket moldboards or a model-year change. The second is measuring only the hole diameter, which leaves spacing and row position to the supplier’s interpretation and produces a blade that mounts but does not sit correctly.

The third is accepting a near match on a retrofit. A pattern that is close but not within tolerance will force the fasteners to pull the segment into position, which distorts the flex element and alters how the blade deflects. The fourth is failing to check the mounting face. A face that has distorted around the holes will not hold a correctly made segment, and no pattern specification corrects it.

The costs appear at the worst time. A pattern error is discovered during fitting, when the vehicle is needed and the workshop has no option except to make the part fit or to put the blade back. A measurement exercise covering each plow group, completed once, removes that risk and produces the record every subsequent order depends on.

A fifth error is worth naming because it outlives the people who made it: accepting a workaround during fitting and not recording it. Where a hole is dressed or a shim is added to make a segment fit, the machine no longer carries the pattern the fleet recorded, and the next order is placed against a specification that is no longer true. Writing the workaround into the record, with the reason, keeps the pattern documentation honest.

Writing the Pattern Requirement Into a Tender

A tender should state the pattern in measurable terms: hole diameter, centre-to-centre spacing, row count and the distance from the top edge to the first row, together with the tolerance accepted at those features and the requirement that the segments seat flat without force. Add the installed length and segment arrangement, the grade requirement with its properties, and the hardware set.

Where the fleet covers several makes, list the patterns by group and require confirmation for each. Where the programme references published patterns, citing the relevant AASHTO standards and requiring a declaration of conformity keeps offers comparable and gives the receiving inspection a basis for acceptance rather than a visual judgement.