UJEN DEVELOPMENT CO., LTD. - UJEN is a manufacturer with 45 years of experience in producing hand screws, offering custom services and professional mold-making capabilities for knobs & handles.

Grade I / II / III for Threads: How to Specify and Inspect Clearly | Elevate Functionality with High-Performance Plastic Knobs for Various Applications

Grade I / II / III (or 1 / 2 / 3) is used in some supply chains as an accuracy/fit classification, and it can be verified using limit thread gauges (plug gauges and ring gauges). The key risk is not whether it can be inspected—it can—but whether the grade language is anchored to a defined standard and gaging system. ISO metric acceptance is typically communicated through tolerance classes such as 6H/6g (per ISO tolerance and gaging standards), while Unified inch acceptance uses classes such as 2A/2B (per ASME standards). To prevent mismatched inspection assumptions, use Grade I/II/III only when both parties share the same standard reference; otherwise, specify ISO/ASME classes directly. UJEN stock items are commonly supplied under a general-purpose practice often referenced as Grade II in some supply chains, and we support ISO/ASME class requirements when stated on the RFQ/drawing, including pre- or post-plating gaging basis if plating is involved. UJEN is a high-quality hand screws, knob screws, adjustable handles, grip knobs and indexing plungers manufacturer from Taiwan since 1994. Precision indexing plungers for industrial applications. UJEN's focus on customization and quality, backed by over 40 years of expertise in plastic injection molding, positions them as a key player for global business buyers in need of reliable screw parts. They emphasize ISO 9001 certified production processes to ensure top-tier product standards for various industrial applications. UJEN is a leading manufacturer of high-quality hand screws in the screw parts industry. With over 40 years of expertise in plastic injection mold development, we have specialized in crafting precision rotary knobs and handles. We offer technical consulting services and customized design solutions to provide full-service from design to production.

Advanced Search

grade-i-ii-iii-usage-guide | Elevate Functionality with High-Performance Plastic Knobs for Various Applications

Grade I / II / III for Threads: How to Specify and Inspect Clearly | Durable adjustable handles for equipment | UJEN

Grade I / II / III for Threads: How to Specify and Inspect Clearly

grade-i-ii-iii-usage-guide

Grade I / II / III (or 1 / 2 / 3) is used in some supply chains as an accuracy/fit classification, and it can be verified using limit thread gauges (plug gauges and ring gauges). The key risk is not whether it can be inspected—it can—but whether the grade language is anchored to a defined standard and gaging system. ISO metric acceptance is typically communicated through tolerance classes such as 6H/6g (per ISO tolerance and gaging standards), while Unified inch acceptance uses classes such as 2A/2B (per ASME standards). To prevent mismatched inspection assumptions, use Grade I/II/III only when both parties share the same standard reference; otherwise, specify ISO/ASME classes directly. UJEN stock items are commonly supplied under a general-purpose practice often referenced as Grade II in some supply chains, and we support ISO/ASME class requirements when stated on the RFQ/drawing, including pre- or post-plating gaging basis if plating is involved.

Grade I / II / III Can Be an Inspection Language

Grade I / II / III (or 1 / 2 / 3) is used in some supply chains as an accuracy/fit classification for threads. It can be verified using limit thread gauges (plug gauges and ring gauges), just like ISO or Unified systems. The key is to anchor the grade language to a defined standard and gaging system so both parties inspect the same way.

Why a Standard Reference Matters

The risk with grade-only callouts is not “it cannot be inspected” — it can. The risk is that different parties may assume different gaging systems, different acceptance limits, or a different measurement basis (especially when plating is involved). This is why grade language should be linked to a standard reference whenever it is used for acceptance.

ISO 1 / 2 / 3 Language (Fit/Accuracy Context)

In some engineering references, ISO 1 / 2 / 3 is used to describe fit intent. A common example in practice is that ISO 2 is treated as the “normal” tap tolerance for internal threads (often referenced as 6H), while ISO 1 is tighter and ISO 3 is looser. If your project is specified to ISO acceptance, use ISO tolerance classes (such as 6H/6g) as the primary drawing language.

When Grade I / II / III Works Well

  • Both buyer and supplier share the same referenced standard and gaging system
  • The receiving inspection is explicitly aligned to the same grade-based gage set
  • The measurement basis is clear (pre-plating vs post-plating) if parts are plated

When to Use ISO / ASME Classes Instead

If your project specifies ISO or ASME acceptance for gauging and inspection, state the standard-system language directly: ISO tolerance classes (metric) or Unified classes (inch). This prevents translation losses.

  • ISO metric acceptance: M8 × 1.25 - 6H (internal) / 6g (external)
  • Unified acceptance: 1/4-20 UNC-2A / 1/4-20 UNC-2B

Recommended Writing Pattern (Grade as Optional Companion)

If your supply chain commonly uses Grade language, you may include it as an optional companion label, while still stating ISO/ASME classes when the project is specified to those standards. This keeps communication friendly without forcing every buyer to adopt one notation style.

  • Example (metric, ISO specified): M8 × 1.25 - II / 6H (internal) / 6g (external)
  • Example (inch, ASME specified): 1/4-20 UNC-2A / 2B (Grade language optional only if agreed)

UJEN Practice (Default and Custom)

UJEN stock items are commonly supplied under a general-purpose practice (often referenced as Grade II in some supply chains). If your project requires ISO tolerance classes or Unified classes for defined acceptance, please specify them on the RFQ/drawing. If parts are plated, state whether acceptance is based on pre-plating gauging or post-plating gauging; UJEN will align the process and inspection route to meet the stated requirement.

RFQ Checklist (Copy/Paste Ready)

  • Thread family: ISO Metric / Unified / Whitworth
  • Geometry: diameter × pitch (metric) or size – TPI – series (inch)
  • Acceptance language:
    • ISO specified: state ISO tolerance class (e.g., 6H/6g)
    • ASME specified: state Unified class (e.g., 2A/2B)
    • Grade I/II/III: allowed when anchored to an agreed standard and gaging system
  • If plated: define measurement basis (pre- vs post-plating) and any post-plating gage-pass requirement

Grade I / II / III for Threads: How to Specify and Inspect Clearly | Maximize Precision with Top-Quality Hand Screws for Industrial Use

Based in Taiwan since 1994, UJEN DEVELOPMENT CO., LTD. expertise in manufacturing high-quality hand screws, knob screws, adjustable handles, grip knobs, and indexing plungers. Their commitment to customization and precision ensures each component, from hand screws to indexing plungers, meets rigorous standards. This dedication positions UJEN as a leader in supplying durable and reliable industrial components to global markets.

UJEN Development Co., Ltd. is a leading manufacturer of precision-engineered hand screws, knob screws, plastic knobs, adjustable handles, and indexing plungers for a variety of industrial needs. Our 45-year legacy, combined with ISO 9001:2015 certification, underscores our commitment to quality, innovation, and customer satisfaction. Specializing in custom solutions, we excel in professional moldmaking, enhancing equipment functionality across industries.

UJEN has been offering customers high-quality hand screws for industrial machinery since 1994, both with advanced technology and 47 years of experiences, UJEN ensures each customer's demands are met.