Hole dimensions and sources

Assembly Hole Series fills every hole size in from the standards below for the thread size and the joint chosen in the dialog. The values are design values copied from the cited pages on 2026-10-26; the standards themselves are paid documents. A size without a sourced row is refused, or keeps the add-in's envelope where that is said below, instead of being guessed. All dimensions are in millimetres.

Metric holes

Size	Close	Normal	Loose	Tap drill	Counterbore, socket head	Counterbore, low head	Counterbore, hex head	Sunk nut with washer	Countersink
M2	2.2	2.4	2.6	1.6	–	–	–	–	4.9
M2.5	2.7	2.9	3.1	2.05	–	–	–	–	6.1
M3	3.2	3.4	3.6	2.5	6.5 × 3.4	6.5 × 2.4	–	–	7
M4	4.3	4.5	4.8	3.3	8 × 4.4	8 × 3.2	13 × 3.2	13 × 4.4	9.2
M5	5.3	5.5	5.8	4.2	10 × 5.4	10 × 3.9	15 × 3.9	15 × 6.1	11.5
M6	6.4	6.6	7	5	11 × 6.4	11 × 4.4	18 × 4.4	18 × 7.2	13.7
M8	8.4	9	10	6.8	15 × 8.6	15 × 5.6	24 × 5.7	24 × 8.8	18.3
M10	10.5	11	12	8.5	18 × 10.6	18 × 6.6	28 × 6.8	28 × 10.8	22.7
M12	13	13.5	14.5	10.2	20 × 12.6	20 × 7.6	33 × 8.1	33 × 13.9	27.2
M14	15	15.5	16.5	12	24 × 14.6	24 × 8.6	–	–	31.2
M16	17	17.5	18.5	14	26 × 16.6	26 × 9.6	40 × 10.6	40 × 18.4	34
M18	19	20	21	15.5	30 × 18.6	30 × 10.6	–	–	–
M20	21	22	24	17.5	33 × 20.6	33 × 11.6	46 × 13.1	46 × 21.6	40.7
M24	25	26	28	21	40 × 24.8	40 × 13.8	58 × 15.8	58 × 26.3	–

Counterbores read diameter × depth. A fine pitch (M8x1 to M24x2) uses the counterbores and countersink of its coarse size and taps at nominal diameter minus pitch.

Clearance holes, ISO 273 (DIN EN 20273): Close, Normal and Loose are the fine, medium and coarse series. TU Darmstadt IIM, clearance holes for screws.
Tap drills, ISO 2306 (DIN 336), for the coarse ISO metric thread. TU Darmstadt IIM, metric ISO thread.
Counterbores for socket heads, DIN 974-1 for ISO 4762 (the same diameters serve DIN 6912 and DIN 7984). neue-physik.de, Senkungen, table 353.9; M14 and M18 from schraube-mutter.de, Bohrtabelle für Zylinderschrauben. The M3 diameter is 6.5 at neue-physik.de and 6.0 at schraube-mutter.de; the add-in uses 6.5. M2 and M2.5 have no row: they keep the add-in's envelope, the head diameter plus 1 mm, 0.5 mm deeper than the head.
Counterbores for low heads: a DIN 7984 head is sunk its head height k plus the allowance DIN 974-1 gives an ISO 4762 head of the same size (t minus k), in the same diameter. Head heights from the DIN 7984 table at fasten.it.
Counterbores for hex heads and sunk nuts, DIN 974-2, the series for socket wrenches to DIN 3124, from the same neue-physik.de table. Its depth sinks an ISO 4017 head; a sunk ISO 4032 nut gets the nut height plus the same allowance over the head height, and a washer adds its thickness (ISO 7089). The table has no row for M2 to M3, M14 or M18: a sunk nut is refused there, and a sunk hex head keeps the add-in's envelope.
Countersinks, DIN 74 form F for ISO 10642, 90°: the opening diameter from the Würth DIN 7991 / ISO 10642 page, also printed by TU Darmstadt IIM, countersinks for screws (M3: 6.9 there, 7.0 at Würth; the add-in uses 7.0). Sizes without a row take the head diameter plus 0.3 mm.
Captive nut pockets are not standardized: the ISO 4032 nut, 0.4 mm wider across flats and 0.5 mm deeper.

Thread depth of a tapped end

The thread a screw needs in the tapped part is the minimum engagement of a property class 8.8 screw in that material, from VDI 2230-1:2015 table 6 as printed in the SFS technical handbook (Hoffmann Group), page 153, plus 2 pitches for the entry chamfer and the screw's end (page 154):

Tapped part material	Coarse thread	Fine thread
Steel S235	1 d	1.25 d
Steel S355	0.9 d	1 d
Quenched and tempered steel	0.8 d	0.8 d
Grey cast iron	1 d	1.25 d
Aluminium alloy	1.4 d	1.4 d

The screw is the shortest nominal length that reaches that engagement below the parts it clamps; the thread takes all of its length in the part, and the hole is drilled the overhang e1 of DIN 76-1 (normal case) deeper:

Pitch P	0.35	0.4	0.45	0.5	0.6	0.7	0.75	0.8	1	1.25	1.5	1.75	2	2.5	3
e1	2.1	2.3	2.6	2.8	3.4	3.8	4	4.2	5.1	6.2	7.3	8.3	9.3	11.2	13.1

e1 from TU Darmstadt IIM, thread runouts and minimum screw-in depth. Example: M6 under a 10 mm part in S235 needs 1.0 × 6 + 2 × 1 = 8 mm of thread; the shortest length of at least 18 mm is 20 mm, so the hole has 10 mm of thread and is drilled 10 + 5.1 = 15.1 mm. A part thinner than that is tapped through; when it holds less thread than the engagement, the result says so.

Screw lengths

The nominal lengths of ISO 4762, ISO 4017 and ISO 10642 (no 14, 18, 22 or 75 mm, which only older DIN tables list): 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 180, 200, 220, 240, 260, 280, 300. Not every size is made in every length; check the supplier. A through bolt is long enough for the parts, the washer and the ISO 4032 nut, and two pitches past the nut.

Inch sizes

UNC/UNF #6 to 1/2 inch use the clearance and tap drill values of the connection library (see connection-library.md). No inch counterbore table is sourced, so inch counterbores keep the add-in's envelope (head diameter plus 1 mm, 0.5 mm deeper than the head; heads from the Camcar Socket Screw Technical Manual 2024, table I-3). Inch countersinks are 82° at the flat head's theoretical sharp diameter (Camcar table I-20, ASME B18.3), where a screw with the largest head sits flush. A sunk nut and a DIN 7984 low head are not offered in inch sizes.

What the sizes do not cover

These are design values for the hole. A joint that carries load still needs its own calculation, for example to VDI 2230, and the supplier's data for the screw, nut and washer you buy: property class, material, finish, and the lengths a size is made in.