The ultra low clearance. But if you buy them new, Lowther america used to gaurantee them. And it;s not that common to have this problem. No...the big problem with lowthers will eb to get a good bo for them. I would suggest go with a horn from theor web site. If you do it right.. i ma sure they will be great...since i see so few used horn lowthers on sale. -akhilesh