Floor Spring Spindle Extension Guide: Floor Level & Door Clearance

05 2026.10
Floor Spring Spindle Extension Guide: Floor Level & Door Clearance

In commercial projects, the Finished Floor Level (FFL) may end up higher than planned because of marble, granite, screed, carpet or other finishes. This can reduce door bottom clearance and create the need for a floor spring spindle extension.

Quick answer: A spindle extension increases the spindle height to match the finished floor and door clearance. It corrects vertical height differences, but does not increase floor spring load capacity.

Quick Selection Summary

  • Standard door bottom clearance: approximately 8–10 mm.
  • Marble, granite, screed or carpet may raise the FFL.
  • Spindle extensions: +5 mm to +50 mm.
  • Confirm model, clearance and installation before ordering.

1. What Is a Floor Spring Spindle Extension?

A floor spring spindle extension (also called an extended spindle or replacement spindle extension) adds height between the floor spring and door system when the Finished Floor Level or door clearance changes. It is commonly used for new installations, replacement work and floor-finish adjustments. CHIEN CHIN offers Exchangeable Spindle Extension in multiple heights.

2. When Is an Extended Floor Spring Spindle Required?

Stone finishes are common in hotels, office buildings, shopping malls and showrooms across India and the Middle East. Common situations include:

  • Marble, granite or stone flooring – the final FFL becomes higher than planned.
  • Thick carpet, screed or raised flooring – the available door clearance decreases.
  • Construction or renovation changes – the final floor level differs from the original setting.
  • Door replacement or maintenance – the new door or replacement spindle must match the existing installation height.

3. How Much Clearance Should Be Left Below the Door?

As a general CHIEN CHIN installation reference, the clearance between the bottom of the door and the finished floor is approximately 8–10 mm under standard conditions.

The purpose of this clearance is to allow the door to open and close without rubbing against stone, carpet or other finished surfaces. If the FFL rises after marble, granite, carpet or another material is installed, the original clearance may become insufficient.

The 8–10 mm figure is an installation reference, not a fixed requirement for every door. Actual clearance should still be checked against the door construction, finished floor height, upper and lower pivot positions and the overall installation. See the CHIEN CHIN Floor Spring FAQ for additional installation information.

4. How Do You Select +5 mm, +10 mm or a Longer Spindle Extension?

CHIEN CHIN exchangeable spindle extensions are available in 5 mm increments from the standard configuration up to +50 mm. The extension value indicates the additional height compared with the standard configuration, while Dimension A refers to the actual dimension shown in the product drawing.

Spindle Specification Extension vs Standard Dimension A
Standard 0 mm 3 mm
+5 mm +5 mm 8 mm
+10 mm +10 mm 13 mm
+15 mm +15 mm 18 mm
+20 mm +20 mm 23 mm
+25 mm +25 mm 28 mm
+30 mm +30 mm 33 mm
+35 mm +35 mm 38 mm
+40 mm +40 mm 43 mm
+45 mm +45 mm 48 mm
+50 mm +50 mm 53 mm

※ Please refer to the latest Exchangeable Spindle Extension product specification before ordering.

3 Steps to Check the Required Spindle Extension

Step 1 | Check the Existing Installation

Measure the actual door bottom clearance and confirm the existing and proposed Finished Floor Level. For a new project, obtain the final flooring thickness and FFL before ordering the spindle extension.

Step 2 | Compare the Door Clearance

Compare the expected clearance with the general 8–10 mm reference and identify the approximate vertical adjustment required.

Step 3 | Confirm Model Compatibility Before Ordering

Match the required adjustment against the available extension sizes, then confirm the original floor spring model, door dimensions and actual installation conditions with the supplier.

Important: A 10 mm increase in finished floor height does not automatically mean that a +10 mm spindle must be ordered. Existing door clearance, door height, pivot alignment and floor spring compatibility should all be checked before the final selection.

5. What Can an Incorrect Spindle Height Cause?

  • Door rubbing: insufficient clearance may cause the door to scrape against marble, granite, carpet or other surfaces.
  • Excessive clearance: incorrect height adjustment may leave an unnecessarily large gap below the door.
  • Poor pivot alignment: a change in door height can affect the relationship between the upper and lower pivot components.
  • Incorrect fitting or abnormal door movement: ordering a spindle without checking the original floor spring model may result in incorrect fitting, rubbing or resistance.

An extended spindle only corrects vertical height differences. It cannot correct an incorrect floor box position, pivot centre, frame alignment or unsuitable floor spring model. If the problem relates to horizontal pivot position, see the Center-Hung vs Offset Pivot Floor Spring Guide. For closing or alignment problems, see Why Is My Floor Spring Not Closing Properly?

6. Which Floor Springs Can Use an Exchangeable Spindle?

CHIEN CHIN offers floor spring models with an exchangeable cam design for applications where replacement or different extension heights may be required. Models currently identified with exchangeable designs include:

For other models such as S275 or S280, please confirm the model and installation requirement before ordering a spindle extension. For load and model comparison, refer to the S200 vs S220 vs S275 vs S280 Floor Spring Selection Guide.

7. What Information Should Importers or Project Buyers Provide Before Ordering?

For replacement parts, project supply or bulk procurement, complete technical information helps reduce incorrect orders and simplifies quotation and spare-parts planning. Please also state whether the order is for a new installation, replacement or maintenance.

  • Original floor spring model
  • Existing spindle or cam dimension, if available
  • Current and new FFL, including the flooring material such as marble, granite, stone or carpet
  • Current door bottom clearance and required height adjustment
  • Door weight and door width
  • Site photos showing the door bottom, floor finish and floor spring cover area
  • Required quantity: project quantity, distributor stock, spare-parts stock, bulk order or container-load shipment

Technical Information Source | CHIEN CHIN Floor Spring & Door Hardware Experience

This guide is based on product specifications and door hardware application experience from CHIEN CHIN, a Taiwan door hardware manufacturer. CHIEN CHIN exchangeable spindle extensions are available from the standard configuration to +50 mm in 5 mm increments, with approximately 8–10 mm door bottom clearance used as a general installation reference.

Actual selection depends on the floor spring model, door dimensions, FFL, pivot alignment and installation conditions. Spindle extensions adjust installation height but do not increase floor spring load capacity.

Learn more about CHIEN CHIN: About CHIEN CHIN｜ Floor Spring Accessories｜ Exchangeable Spindle Extension｜ Certificates & Test Reports

Technical Source: CHIEN CHIN product specifications and door hardware selection data
Content Updated: October 2026

8. Related Products & Technical Guides

9. Floor Spring Spindle Extension FAQ

Q1: When do I need a floor spring spindle extension?

Typical situations include marble or granite flooring, screed, thick carpet, an increased Finished Floor Level, replacement doors with different bottom clearance, or maintenance work where an existing extended spindle must be matched. Stone flooring does not always require an extension: it depends on the final floor height and the door clearance that remains.

Q2: How much door bottom clearance is recommended?

As a general CHIEN CHIN installation reference, approximately 8–10 mm of bottom clearance is used under standard conditions. Actual clearance should be confirmed according to the door, finished flooring and pivot arrangement.

Q3: What spindle extension sizes are available?

CHIEN CHIN exchangeable spindle extensions are available from the standard configuration through +5 mm increments up to +50 mm. The correct size should be selected according to actual clearance, FFL and floor spring compatibility.

Q4: Can spindle extensions from different models be interchanged?

Do not assume interchangeability. Confirm the original floor spring model, spindle dimensions and installation conditions before ordering a replacement spindle extension.

Q5: Does a longer spindle increase floor spring load capacity?

No. Spindle extension changes the installation height; it does not increase the rated door weight or load capacity of the floor spring. Floor spring capacity must still be selected according to the main floor spring model and door specifications.

Need to Source the Correct Floor Spring Spindle Extension?

Send us the original floor spring model, required clearance, finished floor level, spindle dimensions and project quantity. CHIEN CHIN can assist distributors, importers and project suppliers with spindle compatibility, spare-parts planning, bulk orders and container-load shipments.

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