Product Description

A lightweight Grade 9 titanium balance seatpost set designed for Brompton folding bikes. Available in 31.8mm, 33.9mm and 34.9mm diameters with 560mm and 600mm length options, complete with the matching balance-seatpost hardware and base cradle system.

Specifications at a Glance

Variant	Diameter	Length	Seatpost Weight	Listed Kit Hardware Weight	Listed Total System Weight
D31.8 × 600mm	31.8mm	600mm	275g	46g	321g
D33.9 × 560mm	33.9mm	560mm	256g	46g	302g
D33.9 × 600mm	33.9mm	600mm	275g	46g	321g
D34.9 × 560mm	34.9mm	560mm	289g	46g	335g
D34.9 × 600mm	34.9mm	600mm	302g	46g	348g

Seatpost material: Grade 9 Titanium Alloy (Ti-3Al-2.5V)
Minimum wall thickness: 1.0mm
Specified load limit: 80kg
Bolt tool: 4mm Allen key
Base cradle: 1 × Titanium + 1 × free Carbon-Fiber
Application: Brompton folding bikes
Length options: 560mm / 600mm
Diameter options: 31.8mm / 33.9mm / 34.9mm

Weight note: The 46g hardware figure is the listed accessory weight supplied with the corresponding seatpost variant. The individual component weights provided separately do not mathematically reconcile exactly with this 46g figure, so the 46g figure should be treated as the supplier-listed kit hardware weight rather than a calculated sum.

Finish Options by Variant

Finish availability varies by seatpost specification.

D31.8 × 600mm

Gold · Rainbow · Titanium · Black · Blue · Mirror Gold · Mirror Rainbow · Mirror Black · Mirror Blue

D33.9 × 560mm

Gold · Rainbow · Titanium · Black · Blue · Mirror Gold · Mirror Rainbow · Mirror Black · Mirror Blue · Matte Titanium · Matte Black

D33.9 × 600mm

Gold · Rainbow · Titanium · Black · Blue · Mirror Gold · Mirror Rainbow · Mirror Black · Mirror Blue · Matte Titanium · Matte Black

D34.9 × 560mm

Gold · Rainbow · Titanium · Black · Blue · Mirror Gold · Mirror Rainbow · Mirror Black · Mirror Blue · Matte Titanium · Matte Black

D34.9 × 600mm

Gold · Rainbow · Titanium · Black · Blue · Mirror Gold · Mirror Rainbow · Mirror Black · Mirror Blue · Matte Titanium · Matte Black

Matte Titanium and Matte Black are not available for the D31.8 × 600mm variant.

Complete Balance Seatpost Set

The complete set includes the titanium balance seatpost together with its matching mounting hardware and base cradle components.

Included Component	Quantity	Weight	Tool / Compatibility
M5 × 41mm Variable-Diameter Seatpost Bolt	1	3.53g	4mm Allen key
M5 × 47mm Variable-Diameter Seatpost Bolt	1	3.87g	4mm Allen key
M5 × 49mm Seatpost Cradle Clamp	2	6.8g/pc	Fits M5 × 0.8mm bolts
M10 × 65mm Balance Seatpost Center Pin	1	6.8g*	—
3DAM-Specific Seatpost Base Cradle	1	13.3g	—
Carbon-Fiber Seatpost Base Cradle	1	Not specified	Free bonus

* Weight supplied in the original product specification.

The seatpost base cradle has been upgraded to titanium. A carbon-fiber base cradle is included free of charge as an additional piece.

The bolts and individual components included in this set are also available separately in their corresponding product variants, allowing replacement or individual upgrades without purchasing the complete seatpost set again.

Custom Reduced-Shank Titanium Bolts

The kit includes two custom M5 variable-diameter / reduced-shank bolts, available in 41mm and 47mm lengths.

Their reduced-shank construction removes unnecessary material from the bolt body while retaining the required threaded and load-bearing sections.

M5 × 41mm

Weight: 3.53g/pc
Tool: 4mm Allen key

M5 × 47mm

Weight: 3.87g/pc
Tool: 4mm Allen key

These two bolts are also available separately as individual variants.

Saddle Clamp Plates

The kit includes two M5 × 49mm Saddle Clamp Plates.

Weight: 6.8g each
Compatible bolt thread: M5 × 0.8mm

The 49mm dimension refers to the clamp-plate specification, not an M5 × 49mm bolt.

These are clamp plates used within the saddle/balance-seatpost assembly and are not threaded bolts themselves.

They are also available separately.

Balance Seatpost Center Pin

Specification: M10 × 65mm
Weight: 6.8g/pc

The center pin is the central hardware component of the balance-seatpost assembly and is supplied as part of the complete kit.

It is also available separately for replacement purposes.

Titanium Base Cradle + Free Carbon-Fiber Base Cradle

The standard kit now uses an upgraded titanium base cradle.

Titanium Base Cradle

• Weight: 13.3g/pc
• Included as standard

Carbon-Fiber Base Cradle

• 1 piece included free with the complete kit
• Weight: not specified

This gives the complete set two base-cradle material options without requiring a separate purchase for the carbon-fiber component.

Grade 9 Titanium Construction

The seatpost tube is manufactured from Grade 9 Titanium Alloy (Ti-3Al-2.5V).

Grade 9 titanium combines high strength, toughness, corrosion resistance, and low density, making it well suited to lightweight bicycle components where structural performance and weight both matter.

The seatpost features a minimum wall thickness of 1.0mm.

S-PARTS selects Grade 9 titanium for the seatpost tube specifically for its balance of:

• High strength-to-weight ratio
• Toughness and flexibility
• Corrosion resistance
• Low density
• Long-term durability

The specified load limit is 80kg.

Important: The 80kg figure is presented as the product's specified load limit. Please do not interpret it as a separately verified definition of rider weight, total bicycle load, or luggage capacity. Confirm the applicable loading condition with the manufacturer before use if this distinction is important to your application.

Grade 5 Titanium Fastener Material

S-PARTS uses different titanium alloys for different product categories.

The seatpost tube is specified as:

Grade 9 Titanium — Ti-3Al-2.5V

S-PARTS also manufactures titanium fasteners from:

Grade 5 Titanium — Ti-6Al-4V

Grade 5 titanium is widely used for high-performance titanium fasteners because of its high strength and excellent strength-to-weight ratio.

The broader S-PARTS titanium fastener material program specifies Grade 5 titanium with an average tensile strength exceeding 1050 MPa, compared with the commonly referenced minimum tensile-strength level of approximately 895 MPa for Grade 5 titanium.

The individual fastener material specification should be confirmed against the corresponding product variant where required.

Precision Hot Forging & CNC Machining

S-PARTS focuses on controlled manufacturing processes rather than treating titanium hardware as a simple material substitution.

Titanium bolt heads are formed using S-PARTS custom forging dies under approximately 650°C high-temperature processing conditions.

To maintain forging precision and consistency, each dedicated forging die is used for no more than 300 forming cycles before replacement.

The fastener bodies are then machined using precision CNC equipment.

Critical dimensions and threaded features are controlled through a micron-level tolerance management process, helping maintain consistent geometry, thread engagement, and component fit.

For precision titanium hardware, these manufacturing controls are intended to ensure that the finished component performs as precisely as it looks.

Titanium Surface Treatments

S-PARTS offers several titanium surface finishes using different treatment technologies rather than conventional paint.

PVD Vacuum Nitride Coating

Selected finishes, including Gold, Black and Blue, use a PVD vacuum nitride coating process.

The process forms a dense nitride-based surface layer that improves surface hardness and resistance to impact and wear while producing a durable metallic finish.

The resulting color is integrated into the treated surface rather than being created by conventional paint or dye.

Electrolytic Anodizing

Selected titanium colors are produced using electrolytic anodizing.

During the anodizing process, the thickness of the titanium oxide layer is controlled to alter the way incident and reflected light interact.

The resulting optical interference effect creates the characteristic range of titanium colors without the use of conventional coloring dyes.

This is also why anodized titanium can display subtle changes in appearance under different lighting and viewing angles.

Matte Black & Matte Titanium

The Matte Black and Matte Titanium finishes use a combined:

Blasting + Vacuum Nitride Coating

process.

Blasting creates the fine matte texture and distinctive tactile surface, while the subsequent vacuum coating provides the final surface finish.

The result is a more subdued, technical appearance compared with polished or mirror-finished titanium.

S-PARTS Titanium Manufacturing

S-PARTS works with a metal-material supply chain serving the aerospace industry in Xi'an and conducts ongoing material comparison and laboratory testing to select titanium materials that meet its internal standards.

From raw material selection to forging, CNC machining, dimensional control, and surface treatment, the manufacturing process is built around consistency rather than simply producing a visually attractive titanium component.

The combination of Grade 9 titanium construction, precision machining, controlled forging, specialized surface treatment, and lightweight hardware defines the S-PARTS approach to high-end titanium bicycle components.

Package Contents

1 × Grade 9 Titanium Balance Seatpost

1 × M5 × 41mm Variable-Diameter Titanium Bolt

1 × M5 × 47mm Variable-Diameter Titanium Bolt

2 × M5 × 49mm Saddle Clamp Plates

1 × M10 × 65mm Balance Seatpost Center Pin

1 × 3DAM-Specific Titanium Seatpost Base Cradle

1 × Carbon-Fiber Seatpost Base Cradle — Free Bonus

Compatibility & Ordering Notes

• Designed for Brompton folding-bike applications.
• Available diameters: 31.8mm / 33.9mm / 34.9mm.
• Available lengths: 560mm / 600mm.
• Available configurations are limited to the five variants listed above.
• Please select the correct diameter and length before ordering.
• The D31.8 × 600mm variant does not include Matte Titanium or Matte Black as finish options.
• The complete kit includes both a titanium base cradle and a free carbon-fiber base cradle.
• The included M5 bolts use a 4mm Allen key.
• The specified product load limit is 80kg.
• Check all dimensions and mounting interfaces against your existing bicycle before installation.
• For individual replacement components, select the corresponding standalone product variant.