Definition of standard metric bolts
The standarized properties of metric bolts are specified in the international standard ISO 8981:2009 'Mechanical properties of fasteners made of carbon steel and alloy steel  Part 1: Bolts, screws and studs with specified property classes  Coarse thread and fine pitch thread'.
According to ISO 8981 the bolts are characterized depending on their pitch thread:

Course pitch thread: For general applications course pitch thread bolts are used.
They are designated by their nominal diameter d in mm prefixed by the letter 'M'.
The standard course pitch thread metric bolt sizes are: M3, M3.5, M4, M5, M6, M7, M8, M10, M12, M14, M16, M18, M20, M22, M24, M27, M30, M33, M36, M39.

Fine pitch thread: For special applications fine pitch thread bolts may be used.
They are designated as above also including the pitch of thread in mm e.g. M8 × 1, M14 × 1.5, M27 × 2 etc.
In general the stress area of fine pitch thread bolts passing through the threaded part is larger as compared to the course pitch thread bolts.
The calculated strength properties for course pitch thread bolts may be used conservatively for fine pitch thread bolts.
Geometric properties of metric bolts
Nominal diameter
The nominal diameter d is specified in mm as part of the bolt designation, e.g. 8 mm for M8 bolt.
The standard metric bolt diameters are specified in the standard ISO 8981 Tables 4 and 5.
For typical coarse pitch thread bolts the standard sizes are: M3, M3.5, M4, M5, M6, M7, M8, M10, M12, M14, M16, M18, M20, M22, M24, M27, M30, M33, M36, M39.
Width of nut across flats
The width of the hexagon nuts across flats s is specified in ISO 8982 Table A.1 for bolt sizes M5 to M39.
Hole diameter
The design shear resistance of bolts F_{v,Rd} as given in EN199318 Table 3.4 is only valid when the bolt is used in holes with nominal clearance not exceeding the values given in the standard EN 10902 'Requirements for the execution of steel structures', as specified in EN199318 §3.6.1(4).
The resulting hole diameter d_{0} for each type of hole (normal, oversize, short slotted, long slotted) is determined by adding the nominal clearance given in EN 10902 Table 11 to the nominal diameter d of the bolt.
Nominal gross area
The nominal gross area A_{g} corresponds to the crosssectional area of the unthreaded part of the bolt:
A_{g} = π⋅d^{2} / 4
Tensile stress area
The tensile stress area A_{s} corresponds to the reduced crosssectional area inside the threaded part of the bolt.
The tensile stress area depends on the thread and it can be calculated according to ISO 8981 Section 9.1.6.1.
For standard course pitch thread and fine pitch thread bolts the nominal stress area A_{s} is provided in ISO 8981 Tables 4 to 7.
In general the tensile stress area and the shear stress area are different.
According to EN199318 Table 3.4 the shear strength of the bolt may be based on the tensile stress area.
Definition of bolt classes 4.6, 4.8 etc.
The yield strength f_{yb} and the ultimate tensile strength f_{ub} for bolt classes 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, and 10.9 are given in EN199318 Table 3.1.
The first number of the bolt class corresponds to the ultimate strength e.g. 400 MPa for classes 4.x, 500 MPa for classes 5.x, 600 MPa for classes 6.x, 800 MPa for classes 8.x, and 1000 MPa for classes 10.x.
The second number corresponds to the ratio of yield strength to ultimate strength e.g. 60% for class 4.6 leading to a yield strength of 0.60 × 400 MPa = 240 MPa.
Tensile strength of bolts
The tension resistance of the bolt F_{t,Rd} is provided in EN199318 Table 3.4:
F_{t,Rd} = k_{2} ⋅ f_{ub} ⋅ A_{s} / γ_{M2}
where:
 k_{2} is a coefficient that takes values k_{2} = 0.63 for countersunk bolts or k_{2} = 0.9 otherwise.
 f_{ub} is the ultimate tensile strength of the bolt depending on the bolt class (see table above).
 A_{s} is the nominal tensile stress area of the bolt.
 γ_{M2} is the partial safety factor for the resistance of bolts in accordance with EN199318 §2.2(2) Table 2.1 and the National Annex. The recommended value in EN199318 is γ_{M2} = 1.25.
Shear strength of bolts
The shear resistance of the bolt per shear plane F_{v,Rd} is provided in EN199318 Table 3.4:
F_{v,Rd} = α_{v} ⋅ f_{ub} ⋅ A / γ_{M2}
where:
 α_{v} is a coefficient that takes values α_{v} = 0.6 for bolt classes 4.6, 5.6, 8.8 or α_{v} = 0.5 for bolt classes 4.8, 5.8, 6.8 and 10.9. When the shear plane passes through the unthreaded part of the bolt α_{v} = 0.6.
 f_{ub} is the ultimate tensile strength of the bolt depending on the bolt class (see table above)
 A is the appropriate area for shear resistance. When the shear plane passes through the threaded part of the bolt A is equal to the tensile stress area of the bolt A_{s}. When the shear plane passes through the unthreaded part of the bolt A is equal to the gross crosssectional area of the bolt A_{g}.
 γ_{M2} is the partial safety factor for the resistance of bolts in accordance with EN199318 §2.2(2) Table 2.1 and the National Annex. The recommended value in EN199318 is γ_{M2} = 1.25.
Combined shear and tension
The interaction between shear and tension is expressed in EN199318 Table 3.4 according to the following linear relation:
F_{v,Ed} / F_{v,Rd} + (F_{t,Ed} / F_{t,Rd}) / 1.4 ≤ 1.0
where:
 F_{v,Ed} is the applied shear load and F_{v,Rd} is the shear resistance of the bolt.
 F_{t,Ed} is the applied tensile load and F_{t,Rd} is the tension resistance of the bolt.
Bearing strength of bolts
The bearing resistance of the bolt F_{b,Rd} should be verified against the applied shear load F_{v,Ed} in accordance with EN199318 Table 3.4:
F_{b,Rd} = k_{1} ⋅ α_{b} ⋅ f_{u} ⋅ d ⋅ t / γ_{M2}
where:
 f_{u} is the ultimate tensile strength of the connected plate
 d is the nominal diameter of the bolt.
 t is the thickness of the connected plate.
 γ_{M2} is the partial safety factor for the resistance of bolts in accordance with EN199318 §2.2(2) Table 2.1 and the National Annex. The recommended value in EN199318 is γ_{M2} = 1.25.
The coefficient k_{1} is:
for edge bolts: k_{1} = min( 2.8⋅e_{2}/d_{0}  1.7, 1.4⋅p_{2}/d_{0}  1.7, 2.5 )
for inner bolts: k_{1} = min( 1.4⋅p_{2}/d_{0}  1.7, 2.5 )
where e_{2} is the distance between the center of the edge bolt and the end of the plate measured perpendicular to the load transfer direction, p_{2} is the distance between the centers of neighboring bolts measured perpendicular to the load transfer direction, and d_{0} is the diameter of the bolt hole.
The coefficient α_{b} is:
α_{b} = min( α_{d}, f_{ub}/f_{u}, 1.0 )
for end bolts: α_{d} = e_{1}/(3⋅d_{0})
for inner bolts: α_{d} = p_{1}/(3⋅d_{0})  1/4
where e_{1} is the distance between the center of the end bolt and the end of the plate measured parallel to the load direction, p_{1} is the distance between the centers of neighboring bolts measured parallel to the load direction, and d_{0} is the diameter of the bolt hole.
Therefore, based on the equations above, the bearing resistance of the bolt F_{b,Rd} is not affected by the distances e_{1}, p_{1}, e_{2}, p_{2} when the following conditions are satisfied:
for edge bolts: e_{1} ≥ 3.0⋅d_{0} and e_{2} ≥ 1.5⋅d_{0}
for inner bolts: p_{1} ≥ 3.75⋅d_{0} and p_{2} ≥ 3.0⋅d_{0}
Punching strength of bolts
The punching resistance of the bolt B_{p,Rd} should be verified against the applied tensile load F_{t,Ed} in accordance with EN199318 Table 3.4:
B_{p,Rd} = 0.6⋅π ⋅ d_{m} ⋅ t_{p} ⋅ f_{u} / γ_{M2}
where:
 d_{m} is the mean of the across points and across flats dimensions of the bolt head or the nut, whichever is smaller.
 t_{p} is the plate thickness under the bolt or nut.
 f_{u} is the ultimate tensile strength of the steel plate.
 γ_{M2} is the partial safety factor for the resistance of bolts in accordance with EN199318 §2.2(2) Table 2.1 and the National Annex. The recommended value in EN199318 is γ_{M2} = 1.25.
The value of the mean diameter d_{m} is estimated as follows.
The distance across flats s of the nut is given in the standard ISO 8982.
By approximately ignoring the corner rounding for a perfect hexagon the relation of the distance across points s' and the distance across flats s is s' = s / cos(30°) = 1.1547⋅s.
Therefore the mean diameter d_{m} is approximately:
d_{m} = (s + 1.1547⋅ s) / 2 = 1.07735⋅s