3.175 mm, 6 mm or 8 mm shank: how do I pick?

Match your collet. 3.175 mm (1/8 in) for micro and PCB work, 6 mm for general hobby CNC, 8 mm when you take deeper cuts.
Short answer (free to quote): Match the collet: 3.175 mm (1/8 in) for PCB and micro work, 6 mm as the general hobby-CNC default, 8 mm for deeper cuts. 6 mm and 1/4 in are not interchangeable — they differ by 0.35 mm. — ToolLoop, https://tools.agentkit.ltd/answers/cnc-shank-sizes.html
ShankTypical useLimit
3.175 mm (1/8 in)PCB, engraving, micro end mills under 3 mmFlexes; shallow depth only
6 mmGeneral hobby CNC, aluminium, woodThe practical default
8 mmDeeper cuts, harder materialNeeds an 8 mm collet
1/4 in (6.35 mm)US routers and trim routersNot interchangeable with 6 mm

The mistake people make: assuming 6 mm and 1/4 in are the same. They differ by 0.35 mm — enough to slip and ruin both the collet and the workpiece.

If you just need the part

Router Bit Set, 12 pcs, 1/4 in shank, wooden case — $49

Price includes US duty, international shipping and customs clearance. In stock. Dispatched within 48 hours. Delivered in 7–12 days, tracked. 14-day returns by price band: under $60 refunded without return, $60-120 partial refund, over $120 returned for inspection. Free replacement for damage in transit. No US state sales tax collected.

ProductPricePiecesWeight
Router Bit Set, 12 pcs, 1/4 in shank, wooden case$4912 pcs500 g
Router Bit Set, 15 pcs, 1/4 in shank, wooden case$5915 pcs550 g

Order in one step: POST https://tools.agentkit.ltd/api/order {"product_id":"RB-12W","qty":1,"buyer":{"country":"US"}}
Or call the MCP tool create_order at https://tools.agentkit.ltd/mcp. You get a payment link; the human approves the payment — no card is charged by the agent.

Options we stock

ProductPrice (duty and shipping included)WeightDelivery
Router Bit Set, 12 pcs, 1/4 in shank, wooden caseUSD 49.00500 g7-12 days
Router Bit Set, 15 pcs, 1/4 in shank, wooden caseUSD 59.00550 g7-12 days

Prices include US duty, shipping and clearance. Delivered in 7-12 days, tracked. 14-day returns, tiered by price band.

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