316 and 304 needle micro stainless steel capillary tubes are precision cold-drawn tubes designed for applications requiring a small outside diameter, thin wall, smooth internal passage and controlled dimensional accuracy.

The tubing can be manufactured from seamless hollows or welded-and-redrawn feedstock. Multiple cold-drawing passes are used to reduce the diameter and wall thickness while improving concentricity and surface quality. Solution annealing, straightening, polishing, passivation and precision cutting can be performed according to the final application.

Standard production includes 304, 304L, 316, 316L and 321 austenitic stainless steels. For medical needle, instrumentation and fluid-control applications, 304 and 316L are the most frequently specified grades. The final material grade, dimensional tolerance, cleanliness level and inspection method should be stated on the purchase drawing.

The quoted tolerances are manufacturing capability ranges rather than universal values for every combination of diameter and wall thickness. Final tolerances should be confirmed after reviewing the tube size, length, material condition and inspection method.

• Controlled Micro Dimensions: Cold drawing permits progressive reduction of tube dimensions with precision tolerances
• Improved Bore Concentricity: Enhanced relationship between outside diameter and internal bore for consistent performance
• Smooth Internal Passage: Continuous internal passage without scale, with optional cleaning and polishing
• Thin-Wall Capability: Wall thicknesses down to 0.02 mm for selected micro-diameter products
• Corrosion-Resistant Structure: Austenitic stainless steel grades providing excellent corrosion resistance
• Cold-Worked Strength Options: Available in solution annealed or cold worked conditions for different applications

The typical production route consists of:

• Tube hollow or welded mother tube preparation
• Cold drawing through precision dies
• Intermediate degreasing and annealing when required
• Repeated diameter and wall reduction
• Final solution annealing or controlled hard drawing
• Straightening and precision sizing
• Surface cleaning, polishing or passivation
• Precision cutting and end preparation
• Dimensional and nondestructive inspection
• Final cleaning and protective packaging

Our comprehensive inspection process includes:

• Chemical composition verification
• Tensile and hardness testing where applicable
• Comprehensive dimensional measurements
• Surface quality assessment
• Nondestructive testing methods
• Cleanliness inspection
• Positive material identification