Thumb Screws, Flat Spade Head manufactured in A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) are dimensioned to Trade series (spade-head hand screw). The sections below give the mechanical and physical properties of the grade, its behavior in corrosive and elevated-temperature service, and the full size table.
Why Choose A4 Stainless Steel for Thumb Screws, Flat Spade Head
Specified for marine, coastal and chemical applications. For thumb screws, flat spade head, this matters when superior, including marine and chloride environments is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Superior, including marine and chloride environments |
Corrosion Behavior in Service
A4 (316) adds 2–3% molybdenum to the A2 (304) composition, which dramatically improves resistance to chloride-pitting corrosion. For Thumb Screws, Flat Spade Head in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Comparable Grades
For Thumb Screws, Flat Spade Head, the alternative stainless grade is A2 (304). The practical dividing line is chlorides: A2 (304) is fine until salt is involved, and A4 (316) exists for the cases where it is — coastal, marine and road-salt service. Neither reaches the strength of a plated class 8.8 or 10.9 fastener.
Using Stainless Fasteners in Aluminum
Expect the aluminum to corrode, not the fastener — stainless sits higher in the galvanic series, so the aluminum is the one that gives up material. A small fastener in a thick section spreads the loss over a large area and is usually fine; a large fastener in thin sheet concentrates it and is not. Keep water out of the joint, or isolate the two metals with a nylon or coated washer and a sealant.
Sizes of Thumb Screws, Flat Spade Head Available in A4 Stainless Steel
| Thread size | Pitch (mm) | Blade width dk (mm) | Blade height k (mm) | Blade thickness (mm) | Common length range (mm) | Material | Finish |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 10 | 8 | 2.0 | 6~20 | Steel / A2 | Zinc / plain |
| M4 | 0.7 | 12 | 10 | 2.5 | 8~25 | Steel / A2 | Zinc / plain |
| M5 | 0.8 | 15 | 12 | 3.0 | 8~30 | Steel / A2 | Zinc / plain |
| M6 | 1.0 | 18 | 14 | 3.5 | 10~40 | Steel / A2 | Zinc / plain |
| M8 | 1.25 | 22 | 17 | 4.0 | 12~50 | Steel | Zinc |
