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About Rounded Head Screws
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Tamper-Resistant Asymmetrical Drive Button Head Screws
These button head screws have a unique drive that is sold only by McMaster-Carr, making them difficult to remove without a special driver bit (sold separately). Made from 18-8 stainless steel, they have good chemical resistance and may be mildly magnetic. Length is measured from under the head.
Screws | Driver Bits | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Lg. | Threading | Head Dia. | Head Ht. | Drive Size | Tensile Strength, psi  | Specifications Met | Pkg. Qty. | Pkg. | Each | ||
18-8 Stainless Steel | |||||||||||
1/4"-20 | |||||||||||
| 1/2" | Fully Threaded | 0.437" | 0.132" | U25 | 70,000 | ASME B18.3 | 5 | 000000000 | 000000 | 000000000 | 000000 |
| 3/4" | Fully Threaded | 0.437" | 0.132" | U25 | 70,000 | ASME B18.3 | 5 | 000000000 | 00000 | 000000000 | 00000 |
| 1" | Fully Threaded | 0.437" | 0.132" | U25 | 70,000 | ASME B18.3 | 5 | 000000000 | 00000 | 000000000 | 00000 |
| 1 1/4" | Fully Threaded | 0.437" | 0.132" | U25 | 70,000 | ASME B18.3 | 5 | 000000000 | 00000 | 000000000 | 00000 |
| 1 1/2" | Fully Threaded | 0.437" | 0.132" | U25 | 70,000 | ASME B18.3 | 5 | 000000000 | 00000 | 000000000 | 00000 |
Asymmetrical Bits
Turn screws that have the tamper-resistant asymmetrical drive exclusive to McMaster-Carr. Also known as insert bits, use these in hand drivers or with a bit adapter in power tools.
| For Drive Size | Overall Lg. | Material | Each | |
1/4" Hex Shank Size | ||||
|---|---|---|---|---|
| U25 | 1" | Steel | 000000000 | 000000 |