Astralpool / Zodiac Lock Ring ZX Filter Graphpearl 7820002
Astralpool / Zodiac Lock Ring ZX Filter Graphpearl 7820002 is temporarily out of stock and will ship as soon as it's available.
Don't Guess - Ask Us!
Don't Guess - Ask Us!
Not sure if it’s the right part? Send us a message and a photo of what you’re replacing, or what you need, and we’ll help make sure you get the right part the first time.
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Delivery and Shipping Info*
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Astralpool / Zodiac Lock Ring ZX Filter Graphpearl 7820002
Astralpool / Zodiac Lock Ring ZX Filter Graphpearl 7820002 is temporarily out of stock and will ship as soon as it's available.
Astralpool ZX / Zodiac ZXC Cartridge Filter Locking Ring (Lock Nut) — 7820002
This is the genuine Astralpool locking ring (lock nut) for the ZX-family cartridge filter, part number 7820002. It is the large threaded ring that clamps the filter lid down onto the tank — supplied on its own, to replace a ring that is cracked, cross-threaded, seized or grinding rather than turning smoothly. One ring fits every filter in the ZX range, from the ZX50 to the ZX310.
- Physically Stocked, unlike most "drop-shipping" websites.
- Shipped from VIC, NSW, WA, QLD
This is the same filter sold under several brands — Astralpool ZX, Hurlcon ZX, Zodiac ZXC, Zodiac ZCF / Titan ZCF, Astral SMART, Filtrite CF and Aquatight. The Zodiac ZXC is simply the Zodiac-badged Astralpool ZX. Ring colour has changed across production runs (grey, graphite / graphpearl, black); current production is black and the fit and thread are unchanged.
Is This Your Ring? — The 290mm ZX Check
One locking ring fits the whole ZX family, so there is no size to choose — but confirm you have a ZX filter and not a look-alike:
- The ZX lid and ring measure about 290mm across. If your ring is roughly 290mm, this fits.
- If it measures about 222mm you have the smaller Hurlcon QX, which uses a different ring and will not fit.
Measure across the widest point of the ring, not the tank rim.
Worked Example
A customer's ZX150 ring has gone brittle and split a lug, so it no longer tightens. They measure it at 291mm — a ZX, not a QX — so this 7820002 ring is correct. Because the split let the lid weep, they fit a new tank O-ring (78110) at the same time.
Fits Across The ZX Range
- Astralpool ZX / Hurlcon ZX: ZX50, ZX75, ZX100, ZX150, ZX200, ZX250, ZX310
- Zodiac ZXC: ZXC50 to ZXC310
- Zodiac ZCF / Titan ZCF: ZCF75 to ZCF200
- Astral SMART: SMART 350 / 450 / 550
- Filtrite CF / Aquatight: ZX-style cartridge filters
Also Damaged The Lid Or Handles?
If the lid, handles or air bleed are also cracked, the complete lid assembly is the better-value fix and includes a new ring: ZX / ZXC lid assembly with handles & locking ring — SP7820502. Weeping only at the seal? You likely need just the tank O-ring — 78110.
Will Not Fit
- Hurlcon QX — 222mm ring, a different filter.
- Astralpool XC — a separate, unrelated filter series. Contact us with your model and a photo.
Part Numbers & Search References
7820002 · SP7820002 · Lock Ring ZX Filter · ZX locking ring · ZX lock nut · Zodiac ZXC lock ring · Hurlcon ZX filter ring · graphpearl ring · 290mm cartridge filter locking ring.
Frequently Asked Questions
Does one ring fit all ZX filters?
Yes. The same locking ring, part 7820002, fits every ZX-family filter from the ZX50 to the ZX310.
My filter is a Zodiac ZXC. Is this the right ring?
Yes. The Zodiac ZXC is the same filter as the Astralpool ZX, just Zodiac-badged, so this ring fits.
My filter is an Astralpool XC. Is this the right ring?
No. The XC is a separate, unrelated filter series and does not use the ZX ring. Contact us with your model and a photo and we will match the correct part.
The ring is a different colour to mine. Will it still fit?
Yes. Colour has changed across production runs. The thread and fit are unchanged; current production is black.
Should I buy the ring alone or the whole lid?
If only the ring is damaged, buy the ring. If the lid or handles are also cracked, the complete lid assembly is better value and includes a new ring.
Manufacturer Catalogues, Diagrams & Part Numbers
Need exploded views, spare part numbers, product numbers, diagrams, or more product information? See the manufacturer catalogues: Astralpool Catalogue 2026 | Zodiac Catalogue 2026
As with all products, these must be diagnosed and fitted by a qualified and experienced person. This is a special-order item.
In plumbing, named sizes are not the actual measurements. A pipe called “50mm” or “2"” does not measure 50 mm across. Instead, it follows nominal sizing, an internationally-standardised naming system.
Use the Outside Diameter (OD) to check your pipe against fittings. Below is a quick reference for common spa & pool pipe sizes:
| Imperial Name | Metric Name | Pipe Diameter (OD) |
|---|---|---|
| 1/2" | 15mm | ~21.2–21.5 mm |
| 3/4" | 20mm | ~26.6–26.9 mm |
| 1" | 25 mm | ~33.4–33.7 mm |
| 1.5" | 40 mm | ~48.1–48.4 mm |
| 2" | 50 mm | ~60.2–60.8 mm |
| 2.5" | 65 mm | ~75.2–75.5 mm |
These are nominal sizes and are designed to fit matching fittings — not to measure exactly what their name suggests. These are based on PVC Pressure Pipe AS/NZ 1477 Dimensions1.
- º Internal diameters vary slightly by manufacturer and class.
- 1 Not all pool/spa fittings match these dimensions exactly. Some do not follow Australian or international standards. Chinese spas may use proprietary fittings.
Understanding Plumbing Sizes & Nominal Measurements
Plumbing sizes can be confusing. PVC and many other pipe systems use nominal sizes—the size is a name, not the exact measured dimension. This convention is used across most pool and spa systems so that pipes and fittings remain compatible.
Why pipe sizes don’t match the measurements
The Nominal Pipe Size (NPS) system standardises pipe dimensions so that pipes, fittings, valves, and accessories interoperate. Plumbers work with these nominal names every day, but DIYers can be tripped up if they try to match by a tape-measure alone.
How to Measure Pipe Correctly
-
Pipe size is identified by:
- The pipe’s Outside Diameter (OD).
- The fitting’s Inside Diameter (ID) (socket opening).
- Pipe Class / Schedule (e.g., Class 9, 12, 18 or Sch 40) relates to wall thickness and therefore the Internal Diameter (ID) and pressure rating.
- The outside diameter of a fitting is not useful (wall thickness varies by manufacturer).
Hose & Tube Dimensions
Common flexible hose sizes used in pool/spa systems (approximate IDs).
| Imperial Name | Metric Name | Inside Diameter (ID) |
|---|---|---|
| 3/8" | 9–10 mm | ~9 mm |
| 3/4" | 19 mm | ~19 mm |
BSP – British Standard Pipe Thread Sizes
BSP thread names are also nominal. The thread OD will not equal the nominal name.
| BSP Thread Size Naming | Outside Diameter (mm / inch) | TPI |
|---|---|---|
| 1/16" BSP | 7.7 mm / 0.304" | 28 |
| 1/8" BSP | 9.7 mm / 0.383" | 28 |
| 1/4" BSP | 13.16 mm / 0.518" | 19 |
| 3/8" BSP | 16.66 mm / 0.656" | 19 |
| 1/2" BSP / 15 mm | 20.99 mm / 0.825" | 14 |
| 5/8" BSP | 22.99 mm / 0.902" | 14 |
| 3/4" BSP / 20 mm | 26.44 mm / 1.041" | 14 |
| 7/8" BSP | 30.20 mm / 1.189" | 14 |
| 1" BSP / 25 mm | 33.25 mm / 1.309" | 11 |
| 1-1/4" BSP | 41.91 mm / 1.650" | 11 |
| 1-1/2" BSP / 40 mm | 47.80 mm / 1.882" | 11 |
| 2" BSP / 50 mm | 59.61 mm / 2.347" | 11 |
| 2-1/4" BSP | 65.71 mm / 2.587" | 11 |
| 2-1/2" BSP | 75.18 mm / 2.960" | 11 |
| 3" BSP | 87.88 mm / 3.460" | 11 |
| 4" BSP | 113.03 mm / 4.450" | 11 |
| 5" BSP | 138.43 mm / 5.450" | 11 |
| 6" BSP | 163.83 mm / 6.450" | 11 |
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7820002