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A 7kg aluminum pier that gives a ZWO AM5N or AM7 a steadier base than a tripod
Why we like the Pier Mount 90:
- Room to spare: it's rated for 90kg (198lb), far more than an AM7 and its 20kg (44lb) no-counterweight payload, so the pier is never the weak link.
- One stiff column instead of three long legs: the 100mm (4") aluminum pillar and short, wide-set legs settle quickly after a slew or a gust of wind.
- Tool-free from us: we replace the hex screws that lock the top plate with lever knobs and nylon washers, so you can set up without a wrench and without scratching the plate.
- Worth knowing: there's no carry case in the box, but the Celestron 34" tripod soft case fits it. With the top plate attached, an AM5N no longer quite fits in its ZWO case.
The William Optics Pier Mount 90 is a portable field pier for ZWO's strain-wave (harmonic) mounts. It replaces the tripod: a red anodized 100mm column sits on three folding legs with spreader arms and leveling feet, and the top plate takes the mount's 3/8" center screw plus three M6 holes for a solid connection. It stands 89.3cm (35") set up, folds to 79.3cm (31"), and weighs about 7kg (15lb), so it carries out to the backyard or a dark site in one hand.
Key specs: 90kg (198lb) load capacity · 100mm (4") aluminum column · 89.3cm (35") set up, 79.3cm (31") folded · 15mm leveling adjustment per foot · 3/8" center thread and three M6 holes · about 7kg (15lb) · fits ZWO AM5N and AM7
The Pier Mount 90 is on display in our Denver store, so you can see it in person before you buy.
When a pier makes sense
- Heavy payloads on an AM7: 130–150mm refractors and 9.25" to 11" SCTs, where a stiffer base means less wobble when you focus or the mount slews.
- Long refractors on an AM5N: the tall column keeps the scope and camera clear of the legs near the zenith, the same problem a pier extension solves on a tripod.
- Windy sites: a single short column with a wide footprint damps vibration faster than a tall tripod, which helps on the open, breezy sites common along the Front Range.
- Uneven ground: each foot adjusts 15mm, so you can level it on a patio, a gravel pad or a sloped campsite.
How it sets up
Unfold the legs until the spreader arms lock, then turn the knurled knob on each foot to level the pier. Attach the top plate to your mount's base with the 3/8" center screw (and M6 screws in the three outer holes if you like), set the mount on the column, and tighten our tool-free lever knobs. Mount the telescope and you're ready to polar align.
Mile High Exclusive: To simplify setup, we have added tool-free attachment knobs along with nylon washers for the top plate, as shown above, to prevent scratches from metal washers.
What to add for the best results
- A mount (required): the ZWO AM5N with TC40 tripod, or the ZWO AM7 with Pier Mount 90 bundle if you're starting from scratch with the larger mount.
- Celestron 34" tripod soft case: fits the folded pier for transport.
- ZWO ASIAIR Plus: runs the mount, camera, guiding and focuser from your phone.
- ZWO 12V 5A power adapter: for backyard use with the ASIAIR and mount.
Pier Mount 90 vs. TC40 tripod vs. PE200 pier extension
| WO Pier Mount 90 | ZWO TC40 tripod | ZWO PE200 extension | |
|---|---|---|---|
| Type | Freestanding pier (replaces the tripod) | Carbon fiber tripod | Riser that goes on a tripod |
| Height | 89.3cm set up, 79.3cm folded | 470–800mm adjustable | Adds 200mm |
| Load rating | 90kg (198lb) | 50kg (110lb) | 50kg (110lb) |
| Weight | About 7kg (15lb) | 2.3kg (5.1lb) | 1.6kg (3.5lb) |
| Best for | The steadiest portable base, especially for an AM7 | Travel and flying with an AM3 or AM5 | More leg clearance on a tripod you already own |
See all mounts and tripods.
What's in the box
- William Optics Pier Mount 90 with folding legs, spreader arms and three leveling feet
- Three metal spike feet for soft ground (swap in for the rubber feet)
- Top plate with 3/8" center thread
- Mile High Astronomy tool-free lever knobs and nylon washers (installed)
The mount, telescope and carry case are sold separately.
William Optics Pier Mount 90 FAQ
Which mounts does it fit?
The top plate has a 3/8" center thread and three M6 holes, which match the base of ZWO's harmonic mounts. We sell it for the AM5N and the AM7, and it's the pier in our AM7 with Pier Mount 90 bundle.
Do I need a pier, or is the TC40 tripod enough?
For an AM5N with a small or mid-size refractor, the TC40 is fine and lighter to travel with. Choose the pier for an AM7, a heavy SCT or a long refractor, or if you image from a windy spot.
Pier Mount 90 or a PE200 pier extension?
The PE200 lifts a mount 200mm on the tripod you already have, which fixes leg strikes for less money. The Pier Mount 90 replaces the tripod entirely and is the stiffer, steadier option.
Does it come with a case?
No. The Celestron 34" tripod soft case fits it well.
Can I level it on uneven ground?
Yes. Each foot has a knurled knob with 15mm of adjustment, enough to level it on a patio, deck or gravel.
Can I see one before I buy?
Yes. The Pier Mount 90 is on display in our Denver store, so you can see it in person before you buy.
Specifications
| Physical | |
|---|---|
| Load capacity | 90kg (198lb) |
| Column (pillar) diameter | 100mm (4") |
| Height | 89.3cm (35") set up; 79.3cm (31") folded |
| Foot adjustment | 15mm per foot |
| Weight | About 7kg (15lb) |
| Material | Aluminum alloy, red anodized column with black legs |
| Mount connection | |
| Top plate | 3/8" center thread and three M6 holes |
| Mounts | ZWO AM5N and AM7 (ZWO harmonic mount base) |
| Mile High Astronomy upgrade | Tool-free lever knobs and nylon washers |
| Model / SKU | YG-PM-90R |