Engineering Communication (Standard Abbereviations)

STANDARD ABBREVIATIONS

Standard abbreviations in draughting are recommended as notes to provided a brief and clear instructions.

Term	Abbreviations		Term	Abbreviations
Across corners	A/C		Manufacture	MFG
Across flats	A/F		Material	MATL
Approved	APPD		Maximum	Max.
Approximate	APPROX		Meter	m
Assembly	ASSY		Mechanical	MECH
Auxiliary	AUX		Millimeter	mm
Bearing	BRG		Minimum	Min.
Centimeter	CM		Nominal	NOM
Centers	CRS		Not to scale	NTS
Center Line	Cl		Number	No.
Center to center	C/L		Opposite	OPP
Chamfered	CHMED		Outer diameter	OD
Checked	CHD		Pitch circle	PC
Cheese head	CH HD		Pitch circle diameter	PCD
Circular pitch	CP		Quantity	QTY
Circumference	OCE		Radius	R
Continued	CONTD		Radius in note	RAD
Counter bore	C BORE		Reference	REF
Countersink	CSK		Required	REQD
Cylinder	CYL		Right hand	RH
Diameter	DIA		Round	RD
Diametrical pitch	DP		Screw	SCR
Dimension	DIM		Serial number	SI. NO.
Drawing	DRG		Specification	SPEC
Equi-spaced	EQUI-SP		Sphere/Spherical	SPHERE
External	EXT		Spot face	SF
Figure	FIG.		Square	SQ
General	GNL		Standard	STD
Ground level	GL		Symmetrical	SYM
Ground	GND		Thick	THK
Hexagonal	HEX		Thread	THD
Inspection	INSP		Through	THRU
Inside diameter	ID		Tolerance	TOL
Internal	Int		Typical	TYP
Left hand	LH		Undercut	U/C
Machine	M/c		Weight	WT

Selection of Fits

From the above it will be realized that are a very large number of combinations of hole deviation and tolerance with shaft deviation and tolerance. However, a given manufacturing organization will require a number of different types of fit ranging from tight drive fits to light running fits for bearing etc. Such a series of fits may be obtained using one of two ISO standard system:

The Shaft Basis System

For a given nominal size a series of fits is arranged for a given nominal size using a standard shaft and varying the limits on the hole.

The Hole Basis System

For a given nominal size, the limits on the hole are kept constant, and a series of fits are obtained by only varying the limits on the shaft.

The HOLE SYSTEM is commonly used because holes are more difficult to produce to given size and are more difficult to inspect. The H series (lower limit at nominal, 0.00) is typically used and standard tooling (e.g. H7 reamers) and gauges are common for this standard.

Clearance Fits ISO Standard "Hole Basis"

 Transition Fits ISO Standard "Hole Basis"

 Interference Fits ISO Standard "Hole Basis"

 Comparative Roughness Value