somewhere on that tractor there will be a I.D. plate with the full technical model number and serial number (usually located in the cavity under the tilting seat). Get that info, pst back and we may be able to help.

Will do, thanks!

Here it is...

Husqvarna Ride Mower
Model Number: YTH 180
(954140109B) (1999-11)

Now,...couldn't find the right part,..my disk has 18 splines!

Here is a link that might be useful: Replacement Parts

Isn't that part of the trans axle which should be a Hydro Gear 314-510?

Here is a link that might be useful: Hydro Gear 314-510

OP - Agree with Bill - Part needs to be ordered from Hydrogear per Husqvarna IPL detail. Try doing a google search for their website.

Thank you all!

The local dealer ordered it for me,...takes about 2 weeks.

Bill, your link with exploded view seems bang on, Rotor Brake,
59, part# 51072