PTO Spline Shaft Tubing – External Spline, Square Bore

External Spline / Internal Square PTO Agricultural Steel Tube

This is a precision-engineered special-shaped seamless steel tube purpose-built for PTO drive shaft applications in agricultural machinery. What sets this tube apart is its distinctive dual-profile geometry: an externally splined outer surface combined with a perfectly square internal bore that runs the full length of the tube. This is not a standard round tube — it is a cold-drawn special section designed to transmit torque, resist rotation, and mate precisely with mating drive components.

The outer profile features multiple longitudinal ridges arranged around the circumference, forming a spline pattern reminiscent of gear teeth. These raised splines provide secure mechanical engagement within a corresponding hub or sleeve, preventing slippage under load. Meanwhile, the square inner passage accepts a matching square drive shaft, creating a positive-lock connection that transfers rotational power with zero backlash. This dual-locking design — spline outside, square inside — makes the tube exceptionally reliable in high-torque, high-vibration agricultural environments.

Manufactured by Hunan Fushun Metal Co., Ltd. under the Fushun Steel Tube brand, this product is available in a range of cold-drawn seamless steel tube grades and custom profile geometries. Every tube is produced to your engineering specifications with tight dimensional tolerances and full material traceability.

Product Appearance

Unique Shape Profile: Spline Outside, Square Inside

The defining characteristic of this tube is its dual-profile cross-section, which combines two distinct geometric features into a single seamless body:

External Spline Profile

The outer circumference is not smooth or cylindrical. Instead, it carries multiple evenly spaced longitudinal ridges — spline teeth — that run parallel to the tube axis along the entire length. These ridges form a gear-like, angular exterior. Each spline lands on a precise pitch circle, with controlled root and crest dimensions. The spline count, pressure angle, and tooth profile are configured to match the customer’s hub or collar interface.

This splined exterior serves three critical functions. First, it locks rotation by mechanically interlocking with a mating splined bore, preventing the tube from spinning freely inside its housing. Second, the raised ridges increase surface grip for clamping or push-fit assemblies. Third, the profile acts as a built-in alignment guide, ensuring the tube can only be inserted in the correct angular orientation — a feature especially valuable during field maintenance of agricultural equipment.

Internal Square Bore

At the geometric center of the tube lies a square-shaped hollow passage that extends continuously from end to end. Unlike conventional round bores, this square cavity provides a flat-sided drive interface. When a square shaft is inserted, the four flat contact surfaces distribute torque evenly across the full face width, eliminating the point-contact stress concentrations typical of round-bore / round-shaft joints.

The square bore is held to tight dimensional tolerances across flats, with sharp, clean corners achieved through precision cold-drawing over a square mandrel. This internal geometry is particularly well-suited to cold-rolled and cold-drawn precision tube applications where consistent internal dimensions are critical for assembly fit and torque transmission.

Together, the external spline and internal square comprise a two-point positive drive system. The outer spline engages the tractor-side or implement-side hub, while the inner square drives the telescoping shaft assembly. This design eliminates the need for keys, pins, or set screws that can fail under sustained vibration and shock loading.

Steel Grades & Material Options

We supply this special-shaped tube in a selection of carbon and alloy steel grades that balance machinability, wear resistance, and torsional strength for PTO drive applications:

• SAE 1045 / EN C45E — A medium-carbon steel offering an excellent balance of strength, toughness, and cost-effectiveness. Widely used for standard-duty agricultural PTO shafts. Supplied in the cold-drawn condition with improved surface finish and dimensional accuracy.
• SAE 4140 / EN 42CrMo4 — A chromium-molybdenum alloy steel with significantly higher hardenability and fatigue resistance. Recommended for heavy-duty PTO applications involving sustained high torque, frequent engagement cycles, or abrasive field conditions. Can be supplied in the quenched and tempered condition for enhanced mechanical properties.

Both grades are produced as seamless cold-drawn mechanical tubing in accordance with ASTM A519 and are also available under DIN 2391 / EN 10305-4 precision tube standards. Alternative grades and custom chemistries are available upon request.

Technical Specifications

This table represents typical capability ranges. Because each PTO tube is produced as a custom special section, final dimensions are governed by the customer’s approved engineering drawing. Our technical team works closely with your design engineers to validate manufacturability before production begins.

Supply Capability & Lead Time

Fushun Steel Tube maintains dedicated cold-drawing lines for special-shaped profiles, including splined and square-bore configurations. Our tooling library covers a broad range of spline geometries, and we regularly invest in new mandrels and dies for customer-specific profiles.

Manufacturing Process & Quality Assurance

Each tube begins as a seamless hollow round, produced from fully killed steel to the specified grade. The round is then cold-drawn through a precision profiled die and over a square mandrel in a single-pass or multi-pass sequence, depending on the reduction ratio required. This process simultaneously forms the external spline teeth and the internal square bore while work-hardening the material for improved mechanical properties.

Quality control is embedded at every stage:

• Incoming material verification — Chemical composition and mechanical properties of the starting hollow are verified against the mill certificate.
• In-process dimensional checks — Spline profile, square bore dimensions, wall thickness, and straightness are monitored during drawing using calibrated gauges and optical measurement systems.
• Non-destructive testing — Each finished tube undergoes eddy current or ultrasonic inspection per the applicable standard to detect surface and sub-surface discontinuities.
• Final inspection — Dimensional verification, visual surface examination, hardness testing, and mechanical property validation (tensile, yield, elongation) on sample coupons from each heat treatment batch.

Every shipment is accompanied by a Mill Test Certificate to EN 10204 3.1, providing full traceability from steel melt to finished tube. Additional testing, including stainless and alloy steel tube grade verification through positive material identification (PMI), is available upon request.

Primary Applications

The external spline / internal square tube is purpose-designed for the agricultural equipment driveline and finds use across a range of machinery categories:

• PTO Drive Shaft Assemblies — Used as the inner or outer telescoping member in power take-off shafts connecting tractors to implements such as rotary tillers, mowers, balers, and spreaders. The splined exterior mates with the universal joint yoke, while the square bore accepts the sliding inner shaft.
• Implement Drive Lines — Transmits power from the PTO stub shaft to gearboxes, pumps, and driven rollers on towed or mounted equipment. The dual-locking geometry ensures reliable torque transfer even when shaft angles change during field operation.
• Custom Driveline Components — Suitable for specialized agricultural, construction, and industrial machinery where a compact, high-torque telescoping shaft assembly is required. Custom spline profiles can be matched to OEM specifications for aftermarket replacement shafts.
• Material Handling & Conveyor Drives — Applied in screw conveyors, auger drives, and rotary feeders where the square bore provides positive drive without requiring keyways or secondary fastening components.

Request a Quotation

Fushun Steel Tube has supplied special-shaped cold-drawn seamless tubes to agricultural equipment manufacturers and driveline specialists worldwide. Whether you need a standard SAE 1045 PTO spline tube or a custom SAE 4140 alloy profile with non-standard spline geometry, our engineering and production teams are equipped to deliver.