HDH and HDW are two block forms within the DLY HD heavy-duty ball linear guideway series. They use corresponding HD rails of the same nominal size, but their block profiles, assembly heights and mounting methods are different.
HDH is a narrower square-type block, while HDW is a wider flange-type block. The choice between them is mainly determined by the moving-platform width, available assembly height, bolt installation direction and surrounding machine structure.
This HDH vs HDW linear guide comparison explains the model codes, load types, mounting methods and practical selection differences between the two block forms.
HDH and HDW at a Glance
| Comparison Item | HDH Square Block | HDW Flange Block |
|---|---|---|
| Block form | Narrow square type | Wide flange type |
| Mounting-platform width | Suitable for narrower platforms | Requires a wider mounting area |
| Combined assembly height | Generally taller for the same nominal size | Generally lower for the same nominal size |
| Available load types | C heavy-load type and H super-heavy-load type | C heavy-load type and H super-heavy-load type |
| Mounting method | A type: mounting from the top | A type: mounting from the top; B type: mounting from the bottom |
| Platform connection | Compact bolt pattern concentrated over the block body | Wider bolt pattern across the flange |
| Primary design priority | Saving horizontal installation space | Reducing assembly height or connecting to a wider platform |
HDH and HDW blocks with the same nominal size and load type can have the same basic dynamic and static load ratings. However, their external dimensions, mounting-hole positions and installation methods are different.
What Does HDH Mean?
HDH identifies the square-type block in the DLY HD heavy-duty ball guideway series:
- HD: DLY heavy-duty ball linear guideway series
- H: Square-type block
The body of an HDH block is relatively narrow and sits above the rail. Threaded mounting holes are provided on the top of the block, and the bolts pass through the moving platform into the block.
This structure is useful when the moving platform is not wide enough to accommodate a flange block. It is also suitable when the block and fastening bolts can be accessed from above during assembly.
Common HDH examples include:
- HDH25CA: square-type block, size 25, heavy-load type, mounting from the top
- HDH25HA: square-type block, size 25, super-heavy-load type, mounting from the top
HDH blocks use the A mounting method. Bottom-mount B-type models are not included in the HDH specification provided by DLY.
What Does HDW Mean?
HDW identifies the flange-type block in the same HD heavy-duty ball guideway family:
- HD: DLY heavy-duty ball linear guideway series
- W: Flange-type block
The HDW body extends outward on both sides to form a wider mounting flange. Compared with an HDH square block of the same nominal size, HDW provides a broader mounting surface and generally has a lower combined assembly height.
The flange structure also provides two mounting options:
- A type: mounting from the top
- B type: mounting from the bottom
Common HDW examples include:
- HDW25CA: flange-type block, size 25, heavy-load type, mounting from the top
- HDW25CB: flange-type block, size 25, heavy-load type, mounting from the bottom
- HDW25HA: flange-type block, size 25, super-heavy-load type, mounting from the top
- HDW25HB: flange-type block, size 25, super-heavy-load type, mounting from the bottom
HDH35CA square block and HDW35HA flange block
How to Read the Model Code
The complete block code identifies the series, block form, nominal size, load type and mounting method.
Example: HDW25HA
HD = heavy-duty ball guideway series; W = flange type; 25 = nominal guideway size; H = super-heavy-load type; A = mounting from the top.
| Code Position | Code | Meaning |
|---|---|---|
| Series | HD | DLY heavy-duty ball linear guideway series |
| Block form | H / W | H = square type; W = flange type |
| Nominal size | 15–65 | Nominal guideway size |
| Load type | C / H | C = heavy load; H = super heavy load |
| Mounting method | A / B | A = mounting from the top; B = mounting from the bottom |
The same letter can have different meanings depending on its position. For example, in HDH25HA, the first H identifies the square block form, while the second H identifies the super-heavy-load type.
Important: The letters C and H describe the load type. They should not be described as merely a short-block class and a long-block class. The super-heavy-load H type does use a longer block body, but its model-code meaning is "super heavy load."
Heavy Load vs Super Heavy Load
Both HDH and HDW are available in C heavy-load and H super-heavy-load versions for most nominal sizes.
The H super-heavy-load block is longer than the corresponding C heavy-load block. The longer internal loaded zone allows more rolling elements to carry the applied force, resulting in higher basic dynamic and static load ratings.
The size 25 data illustrates the difference:
| Model | Block Form | Block Size L × W × H (mm) | Overall Height (mm) | Dynamic Load C (kN) | Static Load C₀ (kN) |
|---|---|---|---|---|---|
| HDH25CA | Square, heavy load | 84 × 48 × 34.5 | 40 | 26.48 | 56.19 |
| HDW25CA | Flange, heavy load | 84 × 70 × 30.5 | 36 | 26.48 | 56.19 |
| HDH25HA | Square, super heavy load | 104.6 × 48 × 34.5 | 40 | 32.75 | 76.00 |
| HDW25HA | Flange, super heavy load | 104.6 × 70 × 30.5 | 36 | 32.75 | 76.00 |
For size 25, corresponding HDH and HDW blocks with the same load type have the same basic dynamic and static load ratings. Their main differences are the block width, block height, overall assembly height, weight and mounting form.
The permissible static moments should still be checked from the technical specifications for the complete model and applied load direction rather than inferred only from the basic load ratings.
Block Width and Assembly Height
The most visible difference between HDH and HDW is the cross-sectional profile.
HDH places the mounting holes within a narrower square body. This reduces the horizontal space required on the moving platform, but the combined rail-and-block assembly is generally taller.
HDW spreads the mounting holes across a wider flange. This requires more horizontal space, but the block has a lower profile and reduces the combined assembly height.
Using size 25 as an example:
- HDH25 block width: 48 mm
- HDW25 block width: 70 mm
- HDH25 combined assembly height: 40 mm
- HDW25 combined assembly height: 36 mm
This difference can determine whether the moving platform clears surrounding guards, motors, ball screws or structural components.
HDW should not be confused with the DLY ED low-profile guideway series. HDW is the flange-block form of the full-size HD heavy-duty series. ED is a separate guideway family designed specifically to reduce assembly height.
Top and Bottom Mounting
In the DLY HD block code, A and B describe the mounting direction.
A Type: Mounting From the Top
For an A-type block, bolts are installed from above the moving platform. The bolts pass through the platform and engage with the threaded mounting holes in the block.
Examples include:
- HDH25CA
- HDH25HA
- HDW25CA
- HDW25HA
B Type: Mounting From the Bottom
For a B-type flange block, bolts are installed from the underside. This configuration is available for HDW blocks and is useful when the top surface of the moving platform must remain clear or cannot be accessed after assembly.
Examples include:
- HDW25CB
- HDW25HB
HDH square blocks in the current DLY specification use the A top-mount configuration. When bottom mounting is required, an appropriate HDW B-type flange block should be evaluated.
Does a Wider Block Improve Stability?
An HDW flange block provides a wider mechanical connection between the block and the moving platform. Its wider bolt pattern may be more convenient for a broad carriage plate and can improve how the platform is connected to the block.
However, the flange block alone does not guarantee better high-speed stability. Actual axis behavior also depends on:
- Distance between the two rails
- Distance between blocks on each rail
- Moving-table rigidity
- Position of the load's center of gravity
- Applied pitch, yaw and roll moments
- Acceleration and deceleration
- Guideway preload
- Mounting accuracy
If the load has a high center of gravity or creates a large overturning moment, changing from HDH to HDW without changing the rail spacing may not solve the underlying design problem. The complete linear bearing arrangement should be evaluated.
Choose HDH When
An HDH square block is generally the more practical option when:
- The moving platform is narrow
- Horizontal installation space is limited
- The greater combined assembly height is acceptable
- Fasteners can be installed from above
- The existing platform uses a square-block mounting pattern
- A compact block body fits the surrounding machine structure more easily
Typical uses include narrow linear modules, CNC auxiliary axes, compact automation mechanisms and machinery with limited space on either side of the rail.
Choose HDW When
An HDW flange block is generally preferred when:
- The moving table is wide enough to accommodate the flange
- A lower combined assembly height is required
- A wider fastening pattern suits the platform structure
- Mounting from the bottom is required
- The top surface of the moving platform must remain clear
- The existing equipment already uses a flange-block mounting pattern
Typical uses include gantry tables, broad machine platforms, packaging machinery, woodworking equipment and automation systems with restricted vertical clearance.
Can HDH and HDW Use the Same Rail?
HDH and HDW blocks within the same HD nominal size are designed for the corresponding HD rail size. For example, HDH25 and HDW25 blocks belong to the size 25 HD guideway family.
However, rail compatibility does not mean the blocks can be exchanged without modifying the moving platform. HDH and HDW differ in:
- Block width
- Block height
- Combined assembly height
- Platform mounting-hole positions
- Available mounting directions
- Space required around the block
Changing from HDH to HDW may lower the moving platform and require a wider mounting pattern. Changing from HDW to HDH may raise the platform and reduce the available mounting area. An adapter plate or redesigned platform may therefore be necessary.
When changing only the block, the rail condition, accuracy grade and preload should also be confirmed. Mixing unmatched components without checking the running condition may lead to excessive clearance or resistance.
What to Check Before Replacement
| Check | Reason |
|---|---|
| Complete model number | Identifies the block form, size, load type and mounting method |
| Rail cross-section | Confirms that the candidate block belongs to the correct rail series and size |
| Combined assembly height | Prevents the moving platform from being installed at the wrong height |
| Block width and length | Confirms clearance around guards, motors and structural parts |
| Mounting-hole spacing | Determines whether the existing moving plate can be reused |
| Top or bottom mounting | Confirms that the correct A or B block is selected and installation access is available |
| Load type | Distinguishes the C heavy-load block from the H super-heavy-load block |
| Load ratings and moments | Ensures the complete model is suitable for the applied forces and moment loads |
| Accuracy and preload | Prevents inconsistent rigidity or running resistance within a multi-block system |
| Seals and lubrication accessories | Accessories may change the overall block length and maintenance arrangement |
When replacing an existing guide block, send the complete model number and installation drawing rather than only the nominal rail size. Photographs can help identify the block form, but dimensional confirmation is still required.
Available HDH and HDW Sizes
The DLY HD guideway family includes nominal sizes 15, 20, 25, 30, 35, 45, 55 and 65.
Size 15 is supplied in the C heavy-load configuration. C heavy-load and H super-heavy-load configurations are available for the larger sizes included in the current DLY specification table.
DLY HD linear guideways can be supplied in C, H, P, SP and UP accuracy grades according to the model and project requirements. Rail length, hole pitch, end distance, block quantity, accuracy and preload should be confirmed before production.
View the DLY HD heavy-duty linear guideway for detailed rail and block specifications.
Conclusion
HDH and HDW belong to the same DLY HD heavy-duty ball linear guideway family, but they solve different installation problems.
HDH is a narrow square-type block designed for compact platforms and mounting from the top. HDW is a wider flange-type block with a lower assembly profile and offers both top-mount A and bottom-mount B configurations.
The C in the model code identifies the heavy-load type, while H identifies the super-heavy-load type. Although an H-type block is physically longer and provides higher basic load ratings, the letter H should be interpreted as "super heavy load," not simply as a block-length class.
For corresponding models of the same nominal size and load type, HDH and HDW can have the same basic dynamic and static load ratings. The final choice should therefore focus on mounting space, assembly height, fastening direction, platform design and the complete load-and-moment requirements.
