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The Kubota part number RP421-66920 is a genuine OEM shim (also called spacer or alignment shim, specifically "SHIM 1.0" or 1.0mm shim). It is a thin washer-like component used to adjust clearance, spacing, or alignment in mechanical assemblies, preventing wear, vibration, or misalignment in pivot points or linkages. This part is commonly used in the boom (or arm/swing bracket) assemblies of Kubota compact/mini excavators to fine-tune pin/bushing tolerances "as required" during assembly or rebuilds.

Specifications

Type: Flat annular shim/spacer (punched steel, not ground).
Thickness (S): 1.0 mm (primary designation as "1.0").
Inner Diameter (D1): 52.5 mm.
Outer Diameter (D2): 98 mm.
Material: Steel (durable, corrosion-resistant for heavy equipment use).
Weight: Approximately 0.041 kg (0.09 lbs per some dealer listings).
Finish/Production: Punched (stamped); plain or coated for industrial durability.
Notes: Sold individually; often paired with a 0.5 mm variant (RP421-66930) for incremental adjustments. Used "as required" (quantity varies by assembly tolerances, typically 1–several per pivot). Easy to install/replace during boom maintenance or rebuilds. Genuine Kubota ensures precise fit and longevity.

Model Usage / Compatibility

This shim is used primarily in Kubota compact/mini excavators (KX and U series), specifically in front attachments like the boom assembly (e.g., pivot pins, bushings, or linkage points for clearance adjustment). It's listed in official Kubota parts diagrams (e.g., G10000/G10001 boom groups) as "as required" for proper fitment. Compatible across various conventional and zero/tight tail swing models from the mid-2000s onward.

Production dates are approximate based on model introduction and ongoing production (many are current or recent legacy models; Kubota updates series but parts like this carry over).

Model/Series	Description/Type	Approximate Production Dates	Notes/Usage Example
KX033-4	Compact excavator (3.3-ton class)	2014 – present	Boom assembly (e.g., G10001 boom, ref. 130 or similar); shim for pin alignment.
KX040-4 / KX040-5	Compact excavator (4-ton class)	2014 – present	Front attachments/boom (e.g., G10001/G10010 boom); used as required in pivots.
KX121-3 / KX121-3S	Compact excavator (12-ton class, older)	~2005 – 2017 (or updates)	Boom assembly (G10000 boom, ref. 190); shim 1.0mm as required for clearance.
KX161-3 / KX161-3S	Compact excavator (larger KX series)	~2000s – 2010s	Boom/pivot points; compatible in similar assemblies.
U35-4	Zero tail swing compact excavator (3.5-ton)	2014 – present	Boom assembly (G10001 boom, ref. ~130); common for alignment in tight swing models.
U48-4 / U48-5	Zero tail swing compact excavator (4-5 ton)	~2010s – present	Front attachments/boom; shim in linkage or pivot.
U50-3 / U50-3A	Compact excavator (5-ton class)	~2000s – 2010s	Boom or arm assemblies; listed compatibility.
U45S	Older zero tail swing variant	~2000s	Similar boom usage.

Broader compatibility: Fits various KX/U series mini excavators (3–5 ton range) with similar boom designs; cross-referenced in dealer catalogs for models like KX121-3 (SN ranges noted in some diagrams, e.g., up to certain prefixes). Not typically for tractors, loaders, or non-excavator equipment.
General range: Primarily 2005–present (peak in 4th/5th generation KX/U series; introduced around mid-2000s with updates to -4/-5 tiers in 2010s+). Legacy part still widely supported for maintenance on active models.