Ein Ondulierstab ist ein Lockenstab. Eigentlich ist es ja eine Rundbürste mit Fön. Aber im Englischen gibt es nur "curling tongs".

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There is difference between curls and waves. "Ondulieren" = in Wellen legen (French "la onde", Latin "unda"), according to Odge dictionary: to marcel one's hair. According to answers.com: mar·cel (mär-sĕl')
n.
A hairstyle characterized by deep regular waves made by a heated curling iron.


v., -celled, -cell·ing, -cels.

v.tr.
To style (the hair) with deep regular waves, using a curling iron.

v.intr.
To make such a hairstyle.

[After Marcel Grateau (1852–1936), French hairdresser.]

I am sure, curling iron or curling tongs will be perfect. Just in case you need to distinguish between curls and waves..

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Hot Tools CURLING IRON MARCEL GRIP 1"
Price Range: $25 - $45
Product rating:
Jumbo 1" Professional Marcel Iron with Rubberized Handle Model 1108R For full curls and waves Professional Features Include: Patented Pulse Auto Heat Control® for high heat, constant heat 10 variable heat settings Locking / rotating Marcel handle Extra

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We are pleased to offer the complete line of CHI Turbo Professional Ceramic Curling Irons. CHI irons provide Ceramic Technology for flash quick heating with the Far Infrared. Now available in a Spring Grip or Marcel Grip with ergonomically designed handle, CHI Professional Ceramic Curling Irons offer a variable heat setting feature to provide you with total control for all your hairstyle needs. Now you can create multitudes of curls, waves, and incredible body to your styles.

CHI TURBO Professional Ceramic Curling Irons are available in Mini ½", Small ¾", Regular 1" and Big 1-1/2" diameter sizes.

NOTE: Marcel Grip style curling irons do not have a spring loaded mechanism and require constant grip pressure by the user to keep the hair between the clamp and the barrel of the iron.
We DO NOT RECOMMEND any Marcel Grip curling iron for an individual to use at home. A Marcel Grip iron is designed to be used by a hairstylist on a client. Please order the Spring Grip style unless you have worked with a Marcel Grip iron before.