# Deck screws #8 and #10: head diameter (0.330 / 0.34 in), six-lobe drive (T20 / T25) and lengths for Simpson Deck-Drive, DWP stainless and GRK

> What is the head diameter and drive size of a #8 or #10 deck screw (T20 or T25), and what lengths do they come in?

- Category: Hardware › Fasteners
- Kind: Standard part
- Basis: Simpson Strong-Tie's Deck-Drive DSV catalog entries (via SC Fastening) and its DWP Wood SS data sheet, GRK's sell sheet (sizes and lengths only), Grabber's basic-diameter table and a SPAX 4.0 mm listing; numbers only
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**Exact dimensions.** True size, with no tolerance added.

## Notes

- Inches unless stated. 'Deck screw' is not a standard: the sizes here are what the makers print. Simpson prints a head diameter of 0.330 in for both the #10 × 2 in and the #8 × 1-1/4 in Deck-Drive DSV (T25 six-lobe, rimmed flat head with nibs, variable thread, high-low point), and 0.34 in for the flat-head DWP Wood SS #8 (T20) and #10 (T25) stainless screws; trim heads are 0.23 in (#7, T15), 0.25 in (#8 and #9, T20) and 0.26 in (#8 Quik Drive painted trim, T20). 0.330 and 0.34 are two makers' lines, not a tolerance range; the sheets give no tolerance.
- Basic screw diameter from Grabber's selection guide: #8 = 0.1640 in and #10 = 0.1900 in (4.17 and 4.83 mm). Thread major, root diameter, thread length, shank diameter and pilot-hole diameters are not printed on any sheet read here, so none is shown; GRK's sell sheet refers to its own product documentation and ICC-ES reports for those. A SPAX universal screw listing prints 4.0 mm thread and 8.0 mm head with a T20 drive and says it needs no pre-drilling in some woods.
- 'Drive' is the hexalobular (Torx) size as the makers print it: T20 and T25 correspond to ISO 10664 sockets 20 and 25; see torx-hexalobular-drive-sizes-iso-10664 for A and B. GRK prints star drive without a size in the sheet read.
- No file: head profile (rim, nibs, bugle or cone), thread form and point are not published as numbers in the sources read. Simpson's catalog page is linked as the maker's product listing; its CAD availability was not checked.
- Wood screws, inch: wood-screws-flat-head-inch (ASME B18.6.1 head and pilot holes); lag screws: lag-screws-hex-inch; metric chipboard screws: chipboard-wood-screws-din-7505.

## Sizes

| line | size | head diameter (in) | head style | drive | lengths (in) |
|---|---|---|---|---|---|
| Simpson Deck-Drive DSV (catalog item DSVR2MB, #10 x 2) | #10 | 0.330 | rimmed flat head with nibs | T25 six-lobe | 2 (item read); other lengths exist |
| Simpson Deck-Drive DSV (catalog item DSVT114R5LB, #8 x 1-1/4) | #8 | 0.330 | rimmed flat head with nibs | T25 six-lobe | 1-1/4 (item read); other lengths exist |
| Simpson Deck-Drive DWP Wood SS, 316 SS, flat | #8 | 0.34 | flat | T20 | 1-1/4, 1-5/8, 2, 2-1/2, 3 |
| Simpson Deck-Drive DWP Wood SS, 316 SS, flat | #10 | 0.34 | flat | T25 | 2, 2-1/2, 3, 3-1/2, 4-1/2 |
| Simpson Deck-Drive DWP Wood SS, 305 SS, flat | #8 | 0.34 | flat | T20 | 1-1/4, 1-5/8, 2, 2-1/2, 3 |
| Simpson Deck-Drive DWP Wood SS, 305 SS, flat | #10 | 0.34 | flat | T25 | 1, 1-1/2, 2, 2-1/2, 3, 3-1/2 |
| Simpson Deck-Drive DWP Wood SS, 305 SS, trim | #7 | 0.23 | trim | T15 | 1, 1-1/4, 1-5/8, 2, 2-1/4, 2-1/2, 3 |
| Simpson Deck-Drive DWP Wood SS, 305 SS, trim | #8 | 0.25 | trim | T20 | 2-1/2, 3 |
| Simpson Deck-Drive DWP Wood SS, 305 SS, trim | #9 | 0.25 | trim | T20 | 3-1/2, 4 |
| Simpson Deck-Drive DWP Wood SS, 316 SS, trim | #7 | 0.23 | trim | T15 | 1-5/8, 2-1/4, 3 |
| Simpson DWP Wood SS, painted heads, trim | #7 | 0.23 | trim (316 SS) | T15 | 2-1/4, 3 |
| Simpson DWP Wood SS, painted heads, trim | #10 | 0.34 | trim (305 SS) | T25 | 2-1/2, 3 |
| Simpson DWP Wood SS, painted heads, flat | #10 | 0.34 | flat (305 SS) | T25 | 2-1/2, 3 |
| Simpson DWP Wood SS, painted heads, trim (Quik Drive) | #8 | 0.26 | trim (305 SS) | T20 (Quik Drive collated screws use BITTX25 per the sheet) | 2-1/2 |
| GRK R4 multi-purpose (sell sheet) | #8 / #9 / #10 / #12 | not in the sheet | — | star drive (not sized in the sheet) | #8 1-1/2 to 2; #9 1-1/2 to 3-1/8; #10 2-1/2 to 4-3/4; #12 5-5/8 to 6-3/8 |
| GRK Fin/Trim head (sell sheet) | #8 / #9 | not in the sheet | trim | star drive (not sized in the sheet) | #8 1-1/2 to 3-1/8; #9 4, 5 |
| GRK RT composite Fin/Trim (sell sheet) | #8 | not in the sheet | trim | star drive (not sized in the sheet) | 2, 2-1/2, 3-1/8 |
| Basic screw diameters (Grabber selection guide) | #8 / #10 | — | — | — | #8 0.1640 in, #10 0.1900 in (basic screw diameter) |

## Where the files are

- SC Fastening (Simpson catalog): [Simpson Strong-Tie Deck-Drive DSV wood screw #10 x 2 in. (DSVR2MB) and #8 x 1-1/4 in. (DSVT114R5LB): head diameter 0.330 in, T25 6-lobe, rimmed flat head with nibs, variable thread, high-low point](https://catalog.scfastening.com/printitem/deck-drive-premium-fasteners/simpson-deck-drive-structural-wood-screws/dsvr2mb?plpver=10) — web — Distributor catalogue page; numbers only
- Simpson Strong-Tie (DWP Wood SS data sheet, hosted on a Shopify CDN): [Strong-Drive / Deck-Drive DWP Wood SS stainless screws: size, head diameter, drive, lengths for flat, trim and painted heads (#7 to #14)](https://cdn.shopify.com/s/files/1/0398/5188/4705/files/DWP_WOOD_SS_Screw.pdf) — web — Maker data sheet; numbers only
- GRK Fasteners (sell sheet via Fastenal): [GRK selector guide: R4 #8 to #12, RSS, Fin/Trim and RT composite screws by size and length (no head dimensions in the sheet)](https://www.fastenal.com/content/public_notes/EB/GRK-sellsheet-2018.pdf) — web — Maker sell sheet; numbers only
- Grabber Construction Products: [Self-drilling screw selection guide: basic screw diameter by normal size, 0 to 3/8 in (cross-check of #8 and #10 diameters)](https://www.grabberpro.com/userfiles/documents/TechnicalDocuments/Manuals/Self-Drilling-Screw-Selection-Guide.pdf) — web — Maker guide; numbers only
- Weinmann + Schanz (SPAX distributor): [SPAX universal screw 4.0 mm thread diameter, 8.0 mm head diameter, T20; no pre-drill diameter given](https://weinmann-schanz.de/de/en/Promotions/pid.1143.1159/agid.37023/ecm.ag/SPAX%C2%AE-universal-screw-thread-%C3%B8-d1-4-0-mm-head-%C3%B8-8-0-mm-standard-packaging.html) — web — Distributor page; numbers only

## Questions

**What bit does a #10 deck screw use?**

T25 six-lobe on Simpson Deck-Drive DSV and DWP #10 screws; #8 DWP screws use T20 (Simpson).

**What is the head diameter of a #10 deck screw?**

0.330 in on the Simpson DSV #10 × 2 in (T25) and 0.34 in on the flat-head DWP Wood SS #10.

**What is the diameter of a #8 and a #10 screw?**

Basic screw diameter 0.1640 in for #8 and 0.1900 in for #10 (Grabber's table).

## Fits with

- [Torx / hexalobular drive sizes T1–T100 (ISO 10664): A and B across lobes, gauge limits for A, B, Ri, Re and depth H, and the screw size each fits](https://xemstudio.com/objects/torx-hexalobular-drive-sizes-iso-10664/)
- [Flat-head wood screws, inch #4–#14 (ASME B18.6.1): body and head diameter, pilot and clearance holes from three sources + envelope models](https://xemstudio.com/objects/wood-screws-flat-head-inch/)
- [Chipboard screws, DIN 7505 (3, 3.5, 4, 4.5, 5, 6 mm): pan, countersunk and oval-countersunk head dimensions, cross recess size + type-B envelope models](https://xemstudio.com/objects/chipboard-wood-screws-din-7505/)
- [Hex lag screws, 1/4 to 1/2 in (ASME B18.2.1): shank, head width and height, pilot holes + envelope models](https://xemstudio.com/objects/lag-screws-hex-inch/)
- [Plywood and drywall sheets: 4 × 8 ft at actual thickness (3/4 in plywood = 23/32 in)](https://xemstudio.com/objects/plywood-and-drywall/)
- [Dimensional lumber: actual sizes of 1x2 to 6x6, 8 to 16 ft (2x4 = 1-1/2 × 3-1/2 in)](https://xemstudio.com/objects/dimensional-lumber/)