ASTM A513 Type 6 special smooth inside diameter tubing

Type 6 is the special smooth inside diameter (SSID) route in the A513 family. It is not a sink-drawn product — sink drawing is Types 3 and 4. Type 6 exists for applications where the inside surface of the tube is the functional surface: the part seals, slides, or pilots on the ID, and ordinary as-welded or drawn ID conditions are not sufficient.

Choose Type 6 when the ID surface condition itself drives the requirement. Choose Type 5 (DOM) when the broader OD/ID/wall dimensional relationship is the critical characteristic and a conventional drawn ID is acceptable.

Producing a special smooth inside diameter requires additional processing and control beyond a standard route, and the specific practice is producer-dependent. Because the ID is the product, requirements for ID surface condition, dimensional control, and verification method must be stated explicitly and agreed with the producer rather than assumed from the type designation alone.

Discuss how the ID surface will be evaluated — the method, location, and acceptance basis — before the first order. An ID-critical product accepted by an OD-focused inspection plan is a dispute waiting to happen.

Typical evaluations include hydraulic and pneumatic cylinder applications and other components whose function depends on the ID surface. Use Type 6 when the ID condition is genuinely the controlling requirement and its cost is recovered in reduced honing, boring, or finishing work. Do not order it reflexively where a Type 5 ID would serve.

Describing Type 6 as sink drawn on drawings or purchase orders (sink-drawn routes are Types 3 and 4); treating Type 6 and Type 5 as interchangeable; leaving the ID acceptance method unstated on an ID-critical order; and omitting condition when the part will be subsequently formed or machined.