Gariiradda birta ah, oo sidoo kale loo yaqaano birta duuban.Birtu waa mid kulul oo qabowna lagu riixay duub.Si loo fududeeyo kaydinta iyo gaadiidka, loona fududeeyo habaynta kala duwan (tusaale ahaan, farsamaynta birta, suumanka, iwm. dusha sare.Sababtoo ah feeraha dushiisa, saxan birta qaabaysan waxay leedahay saameyn liddi ku ah, waxaana loo isticmaali karaa sida dabaqa, kororka warshadda, badhka shaqada, sagxada markabka, sagxada baabuurta, iwm dhumucda aasaasiga ah (ma tirinaynin dhumucda feeraha), waxaana jira 10 tilmaamood oo ah 2.5-8 mm.Lambarka 1-3 waxaa loo isticmaalaa saxan bir ah oo saxan.