Depth Symbol (↧) — How Far the Feature Goes

The ↧ symbol before a value states it is a depth measured from the surface: how far a hole, slot or counterbore extends below the surface it starts from.

Definition

The depth symbol ↧ precedes the depth dimension with no space (↧12), stating that the value applies to the depth of the feature — how far it extends below the surface it starts from. It replaces the word DEEP that older notes spelled out: ⌀8 ↧12 reads as an 8 mm hole, 12 mm deep, in half the characters and with no ambiguity about which value is the depth.

Where the measurement starts

A depth is measured from the outer surface of the part — specifically, the depth of a blind hole is the depth of the full diameter from that surface. On a flat face this is a single unambiguous reading; where the depth would not be clear, as from a curved or angled surface, the standard directs the drawing to dimension the depth with dimension and extension lines rather than notation, so the start and end of the measurement are drawn rather than implied.

Where ↧ appears

• Blind holes — ⌀8 ↧12 is the full-diameter depth from the outer surface
• Counterbores — ⌴⌀15 ↧8 fixes the counterbore depth; where remaining material thickness matters, that thickness is dimensioned instead
• Slots, pockets and milled recesses whose depth is not carried by another view
• Not for through features — a through hole has no depth value; THRU (or the break lines of a section view) carries that meaning

Measurement

Inspection — depth is verified with a depth micrometer or depth gauge seated on the outer surface, or on a CMM by probing the surface and the feature's flat bottom. The full-diameter depth is what the callout governs: a drill point's cone below the measured depth is not part of the value.

Chamfered or countersunk entries — the depth starts where the full diameter begins, below the entry chamfer, not at the outer face.