A spine and a skull that are less than a Rova Kav are Metamei b'Ohel.
Shamai says that a bone from the skull or spine of a Mes is Metamei b'Ohel.
The early elders disputed whether a half of a Kav or a quarter of a Kav of bones from a Mes is Metamei b'Ohel.
The later Beis Din held that a quarter of a Kav is Metamei for eating Terumah and Kodshim and a half of a Kav of bones is Metamei for a Nazir and for eating a Korban Pesach.
A bone the size of a barely is Metamei via touching and carrying but it is not Metamei b'Ohel.
If a few stones are protruding and a Mes is underneath one of them if a Nazir passes under one of the stones he does not have to shave. (1)
R. Yochanan says that if a limb from a Chai or a Mes does not have sufficient flesh it is not Metamei at all even via touching and carrying.
Reish Lakish says that although it does not have sufficient flesh it is Metamei via touching and carrying. (2)
A half of a Kav of bones from a Mes is Metamei b'Ohel, less than that is only Metamei via touching and carrying.
A half of a Log of blood is Metamei b'Ohel.
R. Akiva holds that a Revi'is of blood from two Mesim is Metamei b'Ohel.
A sword that becomes Tamei from a Mes attains the status of the Mes. (4)
A Rova Kav of bones from a Mes is Metamei b'Ohel.
A BIT MORE
1. It is a Safek whether the Nazir passed underneath the stone that is protruding over the Mes, and mi'Safek he does not have to shave.
2. However if it has a bone the size of a barely it is Metamei via touching and carrying but it is not Metamei b'Ohel.
3. However it is not Metamei b'Ohel.
4. Not only a sword but all metal utensils that are Tamei from a Mes attain the status of the Mes and become Avi Avos ha'Tum'ah.
CHEREV HAREI HU K'CHALAL
A sword that became Tamei from a Mes has the same status as the Mes and it is an Avi Avos ha'Tum'ah. Tosfos says that the sword is Metamei b'Ohel, however Rabeinu Bachaye says that it is only Metamei b'Maga and Masa but it is not Metamei b'Ohel. If all metal utensils that came into contact with a Mes were Metamei b'Ohel a Kohen would not be allowed to walk into any house because it would be difficult to find a house that does not contain even one metal utensil that is Tamei from a Mes.
A LIMB WITH INSUFFICIENT FLESH
If a Nazir comes into contact with a limb from a Chai or a Mes that does not have sufficient flesh he does not have to recount his Nezirus. (Rambam Hilchos Nezirus 7:6)