Check documented polisher, backing-plate and pad fit: RUPES LHR15III example
How to confirm that a polisher, backing plate and pad are a documented match, using the RUPES LHR15III, its 980.027N plate and the 9.DA150M foam pad as a worked record.
Contents
The short answer
A backing plate fits a polisher when the polisher's maker names that plate for that machine. A matching thread or similar diameter is not enough. For the RUPES LHR15III, RUPES's 2026 catalogue lists backing plate 980.027N as the supplied plate. It is a 125 mm plate with a hook-and-loop (Velcro) face and an M8 fitting. The same catalogue pairs the machine with the 9.DA150M fine foam pad in kit LHR15III/BAS. If you are considering any other plate or pad, treat it as unresolved until the maker's documentation names your machine and meets the manual's accessory requirements.
Two terms explain why. The backing plate is the disc that screws onto the polisher's drive and carries the pad. The pad is the foam or fiber layer that touches the paint. The LHR15III is a random orbital polisher, often called a DA (dual action) polisher. Its pad spins and also travels in an offset orbit, which the manual gives as 15 mm. A rotary polisher spins on a fixed axis with no orbit. A plate sold as a rotary polisher backing plate therefore tells you nothing about whether it suits the LHR15III. Only a listing for the specific machine does.
What the LHR15III documents specify
The US-market user manual (revision 01, August 2023) gives these specifications for the LHR15III:
- Orbit: 15 mm
- Backing pad diameter: 125 mm
- Polishing foam diameter: 150 mm
- Speed range: 3000–5200 RPM
- Plate design: hook-and-loop face, held on by a fixing screw
- Pad attachment: the polishing pad is pressed onto the plate's hook-and-loop face
The manual also sets general accessory rules. The diameter, thickness and configuration of an accessory must match the tool. Its speed rating must meet the tool's maximum speed, and the range listed above tops out at 5200 RPM. The manual also states that an accessory is not suitable just because it can be attached.
The 2026 catalogue (Ed. 2) adds the part numbers. It lists the LHR15III as a random orbital tool supplied with backing plate 980.027N. Its backing-plate table gives 980.027N as 125 mm, hook-and-loop, M8, and names the tools it serves, including the LHR15III. Other plates in the same table are assigned to other machine generations. Several of them also use M8. A shared thread size is not a cross-model approval, because each plate is tied to the machines listed against it.
Pad diameter: plate size versus working face
A 150 mm pad on a 125 mm plate can look like a mismatch, but this is how the system is documented. The catalogue diagram for the 9.DA150M shows two dimensions. Its upper diameter, the side that meets the plate, is 130 mm. Its working face, the side that touches the paint, is 150 mm. When you compare pads, record both figures and match them against what the machine maker specifies. Do not rely on a single headline size. RUPES does not publish a numeric clearance between the machine body and the pad. Leave that field blank rather than estimating it from nominal dimensions.
The same caution applies to listings for a 5 inch backing plate for a DA polisher. Five inches is 127 mm, and 125 mm plates are often marketed as roughly 5 inch. A nominal size match still does not show that the plate's fitting, thickness or speed rating suits a particular machine.
Build a machine–plate–pad record
Keep one record per combination. Fill each field from the maker's documents, and note where each figure came from. Below is the documented LHR15III combination entered as a worked example.
| Field | LHR15III worked record |
| Machine / model / document revision | RUPES LHR15III; US manual rev. 01, 08-2023; 2026 catalogue Ed. 2 |
| Motion | Random orbital, 15 mm orbit |
| Plate identifier | 980.027N (supplied plate) |
| Machine connection | M8 |
| Plate attachment / diameter | Hook-and-loop face, fixing screw / 125 mm |
| Pad identifier | 9.DA150M fine foam (in kit LHR15III/BAS) |
| Pad upper / working-face diameter | 130 mm / 150 mm |
| Maker clearance instruction | No numeric clearance published (leave blank) |
| Accessory speed rating | Must meet the tool's maximum speed (range tops at 5200 RPM) |
| Document / page | Manual specifications; catalogue kit listing, backing-plate table and pad diagram |
| Status | Documented approval: plate and pad named for this machine |
Example: evaluating a proposed replacement plate
This is an illustrative scenario, not a real product. Suppose a replacement plate is advertised as M8 and 125 mm, the same as 980.027N. Record it as unresolved. It moves to approved only when its maker's documentation names the LHR15III and confirms that the plate's thickness, configuration and speed rating meet the manual's requirements. Matching the thread and diameter of the original does not settle those questions. Do not mark it approved because the nominal numbers agree. The same method applies to plates sold for other machines, such as a DAS6 backing plate. Start a separate record for that machine and fill it only from that machine's documents.
Changing the plate or pad safely
- Disconnect the polisher from power before removing or fitting any accessory.
- Position the plate and tighten the fixing screw as the manual's plate-fitting instructions describe.
- Center the pad and press it onto the plate's hook-and-loop face.
- Before use, confirm the accessory's speed rating meets the tool's maximum speed.
If a plate or pad you already own has no documentation linking it to your machine, use the supplied 980.027N plate and a pad specified by RUPES until you can confirm it. Ask the accessory maker for a written fitment statement that names your polisher model.
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