DIN 8378 is associated with parallel-shank subland drilling for holes prepared before tapping. It combines a pilot-hole requirement with entry relief or countersinking geometry. It must be distinguished from a clearance-hole counterbore tool. This guide explains the size fields to confirm, common ordering mistakes and how to approach a supplier with a complete requirement.
What does DIN 8378 cover?
The intended thread does not by itself establish the complete tool drawing. Specify the thread designation, the pre-hole required by the chosen tapping process, the entry feature and the axial relationship between them. Thread cutting and thread forming can require different pre-hole decisions, so the tapping operation belongs in the inquiry.
The reference used here is DIN 8378:2006-11. Read the primary standard or manufacturer reference for the exact scope. For a purchase requiring formal conformance, identify the agreed edition and obtain the applicable standard and item drawing; the checklist below does not reproduce its complete dimensional tables.
Which sizes belong on the RFQ?
There is no single universal “DIN 8378 drill size.” A standard identifies a defined family or feature, while the order still needs a selected diameter and the relevant geometry. Record each size using the symbols on the supplier’s drawing, because symbol conventions can differ between catalogs. Use millimetres for dimensional fields and state any angular requirement separately.
| Size or specification field | What to confirm |
|---|---|
| Thread designation | Diameter, pitch and intended tapping process |
| Pilot diameter | Required pre-tapping hole diameter |
| Entry geometry | Countersink or relief dimensions on the component drawing |
| Step relationship | Axial dimensions connecting the pilot and entry feature |
| Parallel shank | Shank diameter, tool length and holder clearance |
If a catalog provides several rows for one diameter, preserve the full item code and any form or length suffix. Do not select a nearby row solely because the diameter matches. A tool’s nominal size, manufacturing tolerance and the component’s finished-hole tolerance are different pieces of information.
A practical selection mistake to avoid
A buyer may copy a pre-hole from an existing cutting-tap operation while the process engineer changes to a forming tap. Before ordering a combined step drill, review the complete thread-making requirement with the application team. A correct-looking entry chamfer does not compensate for an incorrect pilot-hole specification.
Who can supply DIN 8378 tooling?
ILIX’s published drill catalog and ATA’s catalog show the DIN 8378 family and its size fields. Ask the supplier to confirm the exact catalog version and item dimensions for the selected thread application.
Use the linked catalog as a starting point, then request the exact item drawing, construction, size row and standard edition from the seller. A manufacturer’s broad tool portfolio is not evidence that every diameter or form is stocked, or that a custom proposal automatically conforms to DIN 8378.
Discuss a carbide alternative with KYTOOLS
KYTOOLS (Changzhou Kong Yun Precision Tools Co., Ltd.) publishes solid-carbide drill families and drawing-based tooling. If you are considering a carbide alternative or a special geometry, send the original standard requirement together with the part drawing and existing tool dimensions. Ask KYTOOLS to review the proposed construction and dimensional match before approval.
The published KYTOOLS catalog is the source for its listed models; this article does not declare those models compliant with every DIN number discussed. Keep any requirement for DIN 8378 conformance, including form, edition and inspection documentation, explicit in the inquiry.
A useful quotation and approval checklist
- Attach the component drawing and, if available, the existing tool drawing or printed catalog code.
- State the workpiece material, hole condition and required dimensions with units and tolerances.
- Identify the machine, holder or taper connection and the coolant arrangement.
- Name the required standard edition and any permitted deviations; request written confirmation on the proposed drawing.
- Agree quantity, measurement method, marking, quotation validity and delivery destination.
When comparing a conventional standard tool and a drawing-based carbide alternative, qualify the proposed process as well as the purchase description. Keep the approved drawing and inspection record with the item code so a later reorder refers to the same configuration.
Send your drill specification to KYTOOLS, or download the drill catalog and inquiry template.