Mercury MerCruiser Gimbal Housing Washer 21900 | Alpha Bravo Sterndrive
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Part Details
- Part Number: 21900 / 12-21900
- Brand: Mercury / Quicksilver
- Type: Flat washer — gimbal housing bolt hardware
- System: Sterndrive transom assembly — gimbal housing bolt hardware stack
- Dimensions: Approx. 1.00 in. × 1.00 in. × 0.10 in.
- GTIN: 745061130609
- Weight: Approx. 0.01 kg
- Used With: Gimbal housing bolt hardware, including nut 34087 (11-34087) in supported assemblies
About This Part
Genuine Mercury / Quicksilver 12-21900 is an OEM flat washer used at the gimbal housing bolt location in selected MerCruiser sterndrive, transom, and gimbal housing assemblies. It works with the related bolt and nut hardware to provide correct load distribution and clamping at a critical structural location in the transom assembly. Mercury diagrams show this washer across a broad range of MerCruiser sterndrives, including Alpha One, Alpha One Gen II, Bravo 1, Bravo 2, Bravo 3, and several earlier MerCruiser drive families. Confirm fitment by the exact MerCruiser serial number and parts diagram before ordering, as washer placement depends on the specific drive, transom assembly, and hardware stack for your serial number range.
Compatible Applications
- MerCruiser Alpha One — gimbal housing bolt hardware
- MerCruiser Alpha One Gen II — gimbal housing bolt hardware
- MerCruiser Bravo 1 / Bravo 2 / Bravo 3 — gimbal housing bolt hardware
- Earlier MerCruiser sterndrives including 120/140, 160, 165, 225-S, 228, 233, 250, 260, 470, 485, 888, 898 — select transom/gimbal housing applications by serial number
- Selected R / MR / Alpha One transom assembly applications
Washer fitment depends on the exact drive model, transom assembly configuration, hardware stack, and serial number range. Always confirm using the MerCruiser serial number and the correct parts diagram for your specific assembly.
When to Replace
Replace this washer if it is:
- Missing from the hardware stack
- Corroded, pitted, or surface-damaged
- Bent, crushed, or distorted from over-torquing or impact
- Worn or thinned at the bearing surface
- Damaged during removal
A washer in poor condition will not distribute clamping load correctly at the gimbal housing bolt location. Given the structural importance of gimbal housing hardware, this washer should not be reused if there is any doubt about its condition.
Installation Notes
Confirm the washer’s exact position in the MerCruiser parts diagram for your drive and serial number before installation. Inspect the associated gimbal housing bolt, nut 34087 (11-34087), mating surfaces, and surrounding transom hardware while the area is apart. Torque the gimbal housing bolt hardware to the specification in the applicable MerCruiser service manual for your drive and transom assembly.
Cross-Reference Part Numbers
- OEM: 12-21900 / 21900
- GTIN: 745061130609
- Related hardware: 11-34087 (nut used with gimbal housing bolt hardware in supported assemblies)
- Note: No confirmed Mercury OEM superseding number identified. 12-21900 and 21900 are the same part in Mercury’s service and base-number formats respectively.
Parts Desk Insight
21900 is a small part, but its location in the gimbal housing bolt stack makes correct identification important. The most common issue is substituting a generic flat washer by size — the OEM part ensures the correct material, thickness, and load distribution for the application. When servicing gimbal housing or transom hardware, replace all washers in the hardware stack rather than reusing old ones, as distorted or corroded washers may not be visually obvious but can affect torque retention over time.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.