Round to Spline Shaft Adapter Size Chart & Guide
Round Bore to Spline Bore Rigid Shaft Adapters provide a dependable way to connect a round keyed shaft to a splined shaft. These adapters are commonly used in hydraulic pump drives, agricultural machinery, industrial equipment, and other power transmission applications.
MDS of Michigan offers rigid shaft adapters in a variety of round bore sizes, spline bore configurations, and overall lengths to match different shaft requirements.
Use the size chart below to compare available adapters by round bore size, spline bore size, overall length, and SKU. Click any SKU to view its corresponding product page.
What Is a Round Bore to Spline Bore Shaft Adapter?
A round bore to spline bore rigid shaft adapter is a mechanical coupling designed to connect two shafts with different end configurations. One side of the adapter features a round bore with a keyway, while the opposite side contains an internally splined bore.
The round bore accepts a compatible keyed shaft, while the spline bore engages a matching externally splined shaft. This allows torque to be transmitted between the two shafts without requiring both shafts to have the same connection style.
These shaft adapters are commonly used when connecting hydraulic pumps, motors, agricultural drives, and other mechanical power transmission equipment.
Available Rigid Shaft Adapter Configurations
Understanding spline bore sizes: An adapter labeled 1-3/8″ x 21SP features a nominal 1-3/8″ spline bore with 21 internal spline teeth. The round bore and spline bore must match the corresponding shafts for proper engagement.
Round Bore to Spline Bore Rigid Shaft Adapter Size Chart
The chart below includes available rigid shaft adapters with round keyed bores and internal spline bores. All dimensions are listed in inches. Select a SKU to view the corresponding product on the MDS of Michigan website.
| Round Bore Size | Spline Bore Size | Overall Length | SKU |
|---|---|---|---|
| 1-1/8″ | 1-3/8″ x 6SP | 5″ | 10220618 |
| 1″ | 1-3/8″ x 21SP | 4-1/8″ | 115-1600 |
| 1″ | 1-3/8″ x 6SP | 4-1/8″ | 114-1600 |
| 1″ | 1-3/8″ x 21SP | 5″ | 10222116 |
| 1″ | 1-3/8″ x 6SP | 5″ | 10220616 |
| 1″ | 1-1/8″ x 6SP | 5″ | 10180616 |
| 15/16″ | 1-3/8″ x 21SP | 4-1/8″ | 115-1500 |
| 15/16″ | 1-3/8″ x 6SP | 4-1/8″ | 114-1500 |
| 15/16″ | 1-3/8″ x 6SP | 5″ | 10220615 |
| 7/8″ | 1-3/8″ x 21SP | 4-1/8″ | 115-1400 |
| 7/8″ | 1-3/8″ x 6SP | 4-1/8″ | 114-1400 |
| 7/8″ | 1-3/8″ x 6SP | 5″ | 10220614 |
| 3/4″ | 1-3/8″ x 21SP | 4-1/8″ | 115-1200 |
| 3/4″ | 1-3/8″ x 6SP | 4-1/8″ | 114-1200 |
| 5/8″ | 1-3/8″ x 21SP | 4-1/8″ | 115-1000 |
| 5/8″ | 1-3/8″ x 6SP | 4-1/8″ | 114-1000 |
All dimensions are in inches. SP indicates the number of spline teeth. Verify the complete shaft and spline specifications before ordering.
How to Choose the Correct Round to Spline Shaft Adapter
Selecting the correct rigid shaft adapter requires matching both shaft connections and confirming the overall length.
- Identify the round shaft diameter: Measure the round keyed shaft and select the corresponding round bore size.
- Confirm the spline shaft diameter: Identify the nominal diameter of the externally splined shaft.
- Count the spline teeth: Verify whether the shaft requires a 6SP or 21SP configuration.
- Check the overall length: Select a 4-1/8″ or 5″ adapter according to the installation requirements.
- Verify shaft compatibility: Confirm the keyway dimensions, spline profile, shaft engagement, and torque requirements.
Common Applications for Rigid Shaft Adapters
Round bore to spline bore rigid shaft adapters are commonly used in hydraulic pump connections, agricultural machinery, industrial power transmission systems, mechanical drives, and equipment repair applications.
They are particularly useful when connecting a keyed round shaft to a splined shaft without modifying the original shaft configurations.
Understanding 6 Spline and 21 Spline Shaft Adapters
Spline count is one of the most important specifications when selecting a shaft adapter. A 6 spline adapter features six internal spline teeth, while a 21 spline adapter features 21 internal spline teeth.
Even when the nominal spline bore diameter is the same, different spline counts are not interchangeable. Always verify the shaft’s spline dimensions and profile before ordering.
Important: Rigid shaft adapters do not compensate for significant shaft misalignment. Proper shaft alignment, compatible spline engagement, and correct installation are essential for reliable operation.
Find Round Bore to Spline Bore Shaft Adapters at MDS of Michigan
MDS of Michigan supplies mechanical, electrical, and rubber power transmission components for industrial, agricultural, and commercial applications. Our selection of rigid shaft adapters includes multiple round bore sizes, spline configurations, and overall lengths to accommodate different equipment requirements.
Whether you are replacing an existing adapter or selecting components for a new application, our experienced Michigan based team can help identify the correct part.
Need Help Finding the Right Shaft Adapter?
MDS of Michigan has supplied quality power transmission products for over 40 years. Our Michigan based team can help you identify the correct round bore, spline configuration, and shaft adapter for your application.
