DC / SDC rear-pull collets

Also called back-pull or pull-back collets. There is no nut at the front — the collet is drawn backwards into the holder body by a screw from the rear. That gives the slimmest nose of any collet system, and it also removes the tolerance that ER users take for granted.

How the rear pull works

An ER collet is pushed forward into a taper by a nut. A DC collet is pulled backwards into a matching taper inside the holder by a draw screw that threads into the back of the collet. Because nothing has to fit around the outside of the nose, the front of the holder can be made very slim — which is the whole reason these exist on drilling and tapping work in tight spaces.

The trade-off is stiffness of a different kind: the collet is being loaded in tension along its axis rather than squeezed by a ring, so the holding depends entirely on the taper fit and on the torque you apply to that screw.

Small series — DC4 to DC12

Body diameter and overall length agreed across four independent maker tables. The rear thread column has only one source — verify before ordering.
Size	Body Ø D (mm)	Length L (mm)	Rear thread (single source)	Bore sizes commonly stocked
DC4 / SDC4	7	31	M4	2, 3, 3.175, 4
DC6 / SDC6	9.6	36	M5	3, 3.175, 4, 5, 6
DC8 / SDC8	15	45	M6	3, 4, 5, 6, 8, 10
DC10 / SDC10	19	52	—	3, 4, 6, 8, 10
DC12 / SDC12	22	60	M8	3, 4, 5, 6, 8, 10, 12

“SDC10” is not one thing — this is the trap on this page. In the small series above, DC10 has a 19 mm body and a 52 mm length (confirmed by two makers). A separate maker publishes an “SDC10” with a 20 mm body and a 40 mm length, sitting at the bottom of a different series that runs SDC10 / SDC16 / SDC20 / SDC25 / SDC32. The same designation, two incompatible products. Always buy the collet against the holder you own, and match body Ø and length to what you can measure.

Large series — SDC16 to SDC32

This series comes from a single maker's table. We could not corroborate it against a second independent source, so treat it as indicative only.
Size	Body Ø (mm)	Length (mm)	Clamping range (mm)
SDC16	28	50	3 – 16
SDC20	32	55	4 – 20
SDC25	40	65	6 – 25
SDC32	50	80	10 – 32

There is no collapse range — this is the part that catches people out

A DC collet does not have an elastic contraction range. That is stated plainly by more than one maker. The consequence is simple and expensive if you miss it: the bore must match the shank. A 6 mm shank needs a DC6-6, not a DC6-5 forced over it. With ER you can usually get away with clamping a fraction under nominal; with DC you cannot. That is also why the larger DC sizes are sold with the clamping range quoted rather than a single bore.

Two related rules follow from the same design:

The tool must be inserted past the effective clamping length inside the bore. Makers publish this length per bore — it grows with the bore size — and a shallow insertion feels tight on the bench and pulls out in the cut.
Use a torque wrench and do not exceed the recommended value by more than about 30%. One maker warns explicitly that over-tightening can deform the holder itself. The torque wrench is usually a separate purchase.

DC compared with ER and C

	DC / SDC (rear pull)	ER	C power
Retained by	Rear draw screw	Front nut	Front nut
Nut at the nose	No	Yes	Yes
Nose clearance	Best of the three	Moderate	Poor
Collapse range	None	≈1 mm	Effectively none
Bore matching	Exact	Tolerant	Exact
Torque control	Required	Hand-tight	Hand-tight
Stated runout	≤0.005 mm (0.003 mm claimed by one maker)	Class-dependent	Not usually stated
Typical work	Drilling, tapping, tight-clearance milling	General purpose	Heavy roughing

Makers describe the rear-pull angle as giving a stronger grip and better repeat accuracy than a front nut, and several quote repeat clamping accuracy of 0.005 mm or better. Those are maker claims on their own holders; we found no independent standard that defines accuracy classes for DC collets the way DIN 6499 does for ER.

Where DC earns its keep

Drilling and tapping in dense setups, where a nut simply will not go — this is the main reason shops adopt it
CNC machining centres and special-purpose machines with tight tool envelopes
High-repeat work where the same bore is used all day and the exact-match requirement costs nothing

If you change diameters constantly, DC is the wrong system: you will own a collet per size and you will tighten each one with a wrench. ER is the better buy for mixed work, and C power is the answer when the problem is grip rather than clearance. SK and OZ are the other two high-grip families worth comparing before you commit.