Extra Heavy Duty (EHD) 35 ton load bearing capacity round Manhole cover providing two nos. foul gas ventilating holes on cover & two no.s special cover lifting Hook 2. Heavy Duty (HD) 20 ton load bearing capacity round Manhole cover providing two nos. foul gas ventilating holes on cover & two no.s special cover lifting Hook 3. Medium Duty (MD) 10 ton load bearing capacity round Manhole cover providing two nos. foul gas ventilating holes on cover & two no.s special cover lifting hook