WIX Filters · 51xxx · return line
51668 filter element: specifications & equivalents
The 51668 is a WIX Filters return-line hydraulic filter element, built with paper media, sized 129 × 77 mm OD × length (ID 75 mm), rated at 25 µm class. Verify against the current manufacturer data sheet before ordering.
Envelope OD × L 129 × 77 mm
Inside diameter 75 mm
Filtration rating 25 µm nom.
Media Paper
Line type return
Catalog verified. Parameters extracted from the manufacturer’s electronic
catalog / official interchange document and checked 2026-09-28. Confidence score 0.90.
Specification table
| Parameter | Value |
|---|---|
| Filter type | return line |
| Media | Paper |
| Filtration rating | 25 µm |
| Rating basis | nominal |
| Outside diameter OD | 129 mm |
| Inside diameter ID | 75 mm |
| Length | 77 mm |
| End caps | open-ended cartridge element (no baseplate) |
| Flow direction | outside-in |
| Integral bypass valve | none (housing/valve-dependent) |
| Seal material | Nitrile (NBR) |
| Manufacturer part no. | 51668 |
| Source catalog | WIX Filters (MANN+HUMMEL): WIX Filters online product catalog |
| Last verified | 2026-09-28 |
Sources: WIX Filters (MANN+HUMMEL) — WIX Filters online product catalog — accessed 2026-09-26.
WIX Filters® and all model designations are trademarks of their respective owners, used here for identification only — ElementRef is an independent reference site, not an authorized WIX Filters distributor.
Dimensional drawing
Dimensions & series range
| Outside diameter | 129 mm (5.079 in) |
| Inside diameter | 75 mm (2.953 in) |
| Overall length | 77 mm (3.031 in) |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| ↔ HF7987 | Fleetguard | partial | Fleetguard's online catalog lists 51668 as an interchange for HF7987. Envelope cross-reference; verify micron grade, collapse rating and seal configuration before substituting. |
| ↔ RLR1201E10B | Filtrec | partial | Filtrec's official Cross Navigator maps FILTER MART 51668 to FILTREC RLR1201E10B as a direct replacement, publishing the FILTREC element's OD/ID/height envelope and media grade. Rated micron differs (25 vs 12 µm) — verify efficiency class and collapse/seal for the housing before substituting. |
Interchange levels: full catalog-confirmed drop-in · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
Full chart: WIX Filters cross reference chart →
How the 51668 model number is decoded
- 51668WIX hydraulic cartridge element part number.
- 129 mm OD / 75 mm IDCartridge envelope (outside/inside diameter); no mounting thread.
- PaperFilter media: Paper.
Typical equipment & applications
- Mobile and industrial hydraulic return circuits
- Construction and agricultural equipment
- Heavy-duty transmission and torque-converter circuits
Selection pitfalls — read before you substitute
- Line type is not interchangeable: return-line cartridges are low-collapse executions that typically tolerate roughly 10–20 bar differential, while pressure-line elements are commonly rated 100–210 bar. Installing a low-collapse element in a pressure housing can rupture the media on cold-start spikes.
- This element has no integral bypass — opening pressure is set by the housing’s reusable bypass valve. Confirm the valve setting (commonly 3.4 bar) is present before fitting.
- “10 µm nominal” and “12 µm at β1000” can describe the very same media — one is reported at β≥200, the other at β≥1000 per ISO 16889. Compare ratings at the same Beta test point, not just the printed micron number.
- This execution uses nitrile (nbr) seals — verify the compound against the fluid data sheet: standard nitrile (NBR) can fail early in phosphate-ester fluids and at sustained high temperature, where fluorocarbon/Viton executions may be required.
- End-cap geometry and the number/position of O-rings block interchange even when OD and length match — visually compare end caps before fitting, especially with aftermarket cartridges.
Frequently asked questions
What are the dimensions of the 51668 filter element?
The published envelope is 129 mm OD × 77 mm length with a 75 mm inside diameter (5.079 × 3.031 in × 2.953 in ID). Confirm against the housing drawing before ordering.
What micron rating does 51668 use?
This element is rated 25 µm (nominal class). Always compare Beta ratings at the same test point: two brands may print different micron numbers for the same physical grade.
What replaces the 51668 filter element?
2 partial match(es) requiring parameter review
How do I read the 51668 part number?
See the designation decoder above: each segment of 51668 encodes size, line type, filtration grade and media/collapse execution.
Is a same-envelope aftermarket element always a drop-in replacement?
No. Matching OD and length only proves the cartridge fits the bowl. End-cap style, seal compound, micron/Beta rating, collapse pressure and bypass configuration must also match; the table above tags every equivalent as full, partial or verify for exactly this reason.
How often should a hydraulic filter element be replaced?
Replace at the housing manufacturer’s recommended differential-pressure setting (commonly signalled by a clogging indicator), or on a time-based service interval when no indicator is fitted — never wait for bypass to open continuously, because unfiltered oil then reaches the valves.
Other models in the 51xxx series
All 306 →Reviewed & verified by the ElementRef engineering desk against WIX Filters (MANN+HUMMEL) on 2026-09-28. Read our editorial & correction policy.