GB/T 3103.3-2020 Flat Washer Tolerances Guide
1. Introduction
Flat washers play a critical role in fastening systems by distributing loads, preventing surface damage, and ensuring assembly integrity. The GB/T 3103.3-2020 standard specifies tolerances for plain flat washers with nominal diameters from 1 mm to 150 mm, applicable to product grades A, C, and F. This standard is essential for maintaining precision in mechanical engineering, automotive, aerospace, and construction industries.
Adopted from ISO 4759-3:2016, it ensures compatibility with international practices, promoting quality control and interchangeability. This guide details tolerances for inner hole, outer diameter, thickness, chamfers, and form/position attributes, aiding engineers in design and procurement.
2. GB/T 3103.3-2020 Standard Overview
Released in 2020 by the Standardization Administration of China, this standard updates previous versions to align with global advancements in fastener technology. It applies to plain washers used with bolts, screws, and nuts, excluding special types like lock washers.
Key content includes dimensional tolerances before surface treatment, with provisions for deviations only when technically justified. Shape and position tolerances follow GB/T 1182 and GB/T 16671.
3. Basic Principles of Flat Washer Tolerances
Tolerances ensure washers fit precisely in assemblies, preventing failures due to misalignment or excessive play. They are defined for product grades: A (precision), C (general), and F (fine). Unless specified otherwise, tolerances apply pre-treatment.
Key parameters include inner diameter (d1), outer diameter (d2), thickness (t), chamfers (c1, c2), and form tolerances like coaxiality and flatness.
4. Detailed Tolerance Specifications
Tolerances for inner hole d1 vary by thickness and product grade.
| Thickness | Tolerances | ||||||
|---|---|---|---|---|---|---|---|
| Product Grade | |||||||
| F | UN | C | |||||
| t < 2 2 ≤ t < 4 t ≥ 4 | d1 Tolerance | T1 minimo | e1 massimo | d1 Tolerance | T1 minimo | e1 massimo | d1 Tolerance |
| H12 | 0.5 t | 0.10 t | H13 | 0.3 t | 0.15 t | H14 | |
| H12 | 0.3 t | 0.15 t | H13 | 0.25 t | 0.20 t | H14 | |
| H13 | 0.2 t | 0.20 t | H14 | 0.2 t | 0.25 t | H15 | |
| Burring not defined but permitted | Tear band (e1), t1 and burring not defined but permitted | ||||||
| T1 is the portion of the hole within the specified tolerance of d1 | |||||||
| Thickness | Tolerances | ||||
|---|---|---|---|---|---|
| Product Grade | |||||
| F | UN | C | |||
| t < 2 2 ≤ t < 4 t ≥ 4 | d2 Tolerance | e2 massimo | d2 Tolerance | e2 massimo | d2 Tolerance |
| h13 | 0.13 t | h14 | 0.18 t | h16 | |
| h13 | 0.15 t | h14 | 0.20 t | h16 | |
| h14 | 0.18 t | h15 | 0.25 t | h16 | |
| Burring and t2 not defined but permitted | Tear band (e2), t2 and burring not defined but permitted | ||||
| T2 is the portion of the outer diameter within the specified tolerance of d2 | |||||
Thickness tolerances measured after deburring.
| Thickness t | Product Grade | ||
|---|---|---|---|
| F | UN | C | |
| t ≤ 0.5 | ±0.04 | ±0.05 | ±0.10 |
| 0.5 < t ≤ 1 | ±0.06 | ±0.10 | ±0.20 |
| 1 < t ≤ 2.5 | ±0.12 | ±0.20 | ±0.30 |
| 2.5 < t ≤ 4 | ±0.16 | ±0.30 | ±0.60 |
| 4 < t ≤ 6 | ±0.20 | ±0.60 | ±1.00 |
| 6 < t ≤ 10 | ±0.24 | ±1.00 | ±1.20 |
| 10 < t ≤ 20 | ±0.28 | ±1.20 | ±1.60 |
| Nominal Thickness | Product Grade | |||||
|---|---|---|---|---|---|---|
| F | UN | C | ||||
| c1 minimo | c2 minimo | c1 minimo | c2 minimo | c1 minimo | c2 minimo | |
| 1 ≤ t < 2 | 0.20 t | 0.25 t | 0.20 t | 0.25 t | 0.20 t | 0.25 t |
| 2 ≤ t < 4 | 0.18 t | 0.22 t | 0.18 t | 0.22 t | 0.18 t | 0.22 t |
| t ≥ 4 | 0.15 t | 0.20 t | 0.15 t | 0.20 t | 0.15 t | 0.20 t |
Upon buyer request, chamfer position relative to stamping deviations should be specified in the order.
Δt applies outside x = 0.1 (d2 – d1), i.e., 60% of ring width.
| Thickness t | Product Grade | ||
|---|---|---|---|
| F | UN | C | |
| Δt massimo | Δt massimo | ||
| t ≤ 0.5 | 0.02 | 0.025 | No requirement |
| 0.5 < t ≤ 1 | 0.03 | 0.05 | |
| 1 < t ≤ 2.5 | 0.06 | 0.1 | |
| 2.5 < t ≤ 4 | 0.08 | 0.15 | |
| 4 < t ≤ 6 | 0.1 | 0.2 | |
| 6 < t ≤ 10 | 0.12 | 0.3 | |
| 10 < t ≤ 20 | 0.14 | 0.4 | |
| Thickness t | Product Grade | ||
|---|---|---|---|
| F | UN | C | |
| y massimo | y massimo | y massimo | |
| t < 2 | 2 IT11 | 2 IT12 | 2 IT13 |
| 2 ≤ t ≤ 4 | 2 IT12 | 2 IT13 | 2 IT14 |
| t ≥ 4 | 2 IT13 | 2 IT14 | 2 IT15 |
| Tolerance y based on diameter d2 | |||
Flatness z is the difference between effective height heff and effective thickness teff. Note: Independent of thickness tolerance; additional processes like grinding may reduce deflection. Measured after deburring.
| Thickness t | Product Grade | ||
|---|---|---|---|
| F | UN | C | |
| z massimo | z massimo | z massimo | |
| t ≤ 0.5 | 0.07 | 0.1 | 0.13 |
| 0.5 < t ≤ 1 | 0.1 | 0.15 | 0.2 |
| 1 < t ≤ 2.5 | 0.2 | 0.2 | 0.25 |
| 2.5 < t ≤ 4 | 0.3 | 0.3 | 0.3 |
| 4 < t ≤ 6 | 0.4 | 0.4 | 0.4 |
| 6 < t ≤ 10 | 0.6 | 0.6 | 0.6 |
| 10 < t ≤ 20 | 1 | 1 | 1 |
5. Key Requirements in GB/T 3103.3-2020
Tolerances must be verified pre-surface treatment. Product standards take precedence if differing. Measurements for thickness and flatness occur post-deburring to ensure accuracy.
6. Precision and Error Analysis
Errors may arise from manufacturing processes like stamping, leading to burring or coaxiality issues. Improve accuracy via precise tooling and post-processing. Common errors include ignoring chamfer specs; resolve by adhering to grade-specific tables.
7. Impact of GB/T 3103.3-2020 on Industry
This standard enhances material research by standardizing tolerances, aids quality control in manufacturing, and supports applications in high-precision sectors like aerospace, where grade A washers ensure reliability.
8. Frequently Asked Questions (FAQ)
What is the difference between product grades A, C, and F?
Grade A offers the tightest tolerances for precision applications, C for general use, and F for fine tolerances in specific scenarios, as detailed in the tables.
When should tolerances be measured?
Tolerances apply before surface treatment, with thickness and flatness measured after deburring to avoid inaccuracies from manufacturing artifacts.
How does this standard compare to ISO 4759-3?
GB/T 3103.3-2020 is equivalent to ISO 4759-3:2016, ensuring global compatibility for tolerances on flat washers.
What if product standards differ from this?
Product-specific standards take precedence, but deviations require technical justification.
Are chamfers mandatory?
Minimum chamfers are specified to prevent sharp edges, with values based on thickness and grade; for combined washers, position may need specification.
How to select the appropriate grade for an application?
Choose based on assembly precision: A for high-load critical parts, C for standard bolting, considering factors like vibration and load distribution.
