TDK Inductors/Coils FAQ: Part Markings

This article will help answer some of the questions customers have asked about common part markings on TDK’s inductors and coils.

What Are the Direction Identification Markings on Some TDK Products For?

An inductor has a winding direction (polarity), and the marking is placed so that the polarity can be confirmed from its external appearance.
Depending on usage conditions, the polarity of the inductor can affect the inductor’s characteristics.

Why Are the Characters Such as “4R7” or “100” Printed on Some Products?

The markings are the inductances expressed in microhenrys (uH).
The first two digits indicate significant figures and the third digit a multiplier. When there is a “R”, it indicates a decimal point. All numbers are significant figures.

4R7 = 4.7 (uH)
100 = 10 × 10^0 = 10 (uH)
101 = 10 × 10^1 = 100 (uH)

Content and images provided courtesy of TDK’s FAQs: