Rotor pair for a compressor block of a screw machine, wherein the rotor pair is comprised of a secondary rotor that rotates about a first axis and a main rotor that rotates about a second axis, wherein the number of teeth (z 2) in the main rotor is 3 and the number of teeth (z 1) in the secondary rotor is 4, wherein the relative profile depth of the secondary rotor PT rel = rk 1 − rf 1 rk 1 is at least 0.5, preferably at least 0.515, and at most 0.65, preferably at most 0.595, wherein rk 1 is an addendum circle radius drawn around the outer circumference of the secondary rotor and rf 1 is a dedendum circle radius starting at the profile base of the secondary rotor, wherein the ratio of the axis distance a of the first axis to the second axis and the addendum circle radius rk 1 a rk 1 is at least 1.636 and at most 1.8, preferably at most 1.733, wherein preferably the main rotor is configured with a wrap-around angle Φ HR, for which it holds that 240° ≤ Φ HR ≤ 360°, and wherein, in a transverse sectional view, a point C is defined on the connecting line ( C 1 C 2) between the first axis and the second axis, at which the pitch circles WK 1 of the secondary rotor and WK 2 of the main rotor touch, that K5 defines the point of intersection of the dedendum circle FK 1 of the secondary rotor with the connecting line ( C 1 C 2), wherein r 1 is the distance between K5 and C, and that K4 designates the point of the suction-side part of the line of engagement which lies farthest spaced apart from the connecting line ( C 1 C 2) between C1 and C2, wherein r 2 is the distance between K4 and C, and wherein it holds that: 0.9 ≤ r 1 r 2 ≤ 0.875 × z 1 z 2 + 0.22 with z 1: number of teeth in the secondary rotor and z 2: number of teeth in the main rotor, and wherein, in a transverse sectional view, circular arcs B 25, B 50, B 75 extending within a secondary rotor tooth are defined, the common center point of which is given by the axis C1, wherein the radius r 25 of B 25 has the value r 25 = rf 1 +0.25*(rk 1 -rf 1), the radius r 50 of B 50 has the value r 50 = rf 1 +0.5*(rk 1 -rf 1), and the radius r 75 of B 75 has the value rf 1 +0.75*(rk 1 -rf 1), and wherein the circular arcs B 25, B 50, B 75 are each delimited by the leading tooth flank F V and trailing tooth flank F N, wherein tooth thickness ratios are defined as ratios of the arc lengths b 25, b 50, b 75 of the circular arcs B 25, B 50, B 75 with ε 1 = b 50 /b 25 and ε 2 = b 75 /b 25, and the following rating is satisfied: 0.65 ≤ ε 1 < 1.0 and/or 0.50 ≤ ε 2 ≤ 0.85, preferably 0.80 ≤ ε 1 < 1.0 and/or 0.50 ≤ ε 2 ≤ 0.79. wherein the number of teeth (z 2) in the main rotor is 3 and the number of teeth (z 1) in the secondary rotor is 4, wherein the relative profile depth of the secondary rotor PT rel = rk 1 − rf 1 rk 1 is at least 0.5, preferably at least 0.515, and at most 0.65, preferably at most 0.595, wherein rk 1 is an addendum circle radius drawn around the outer circumference of the secondary rotor and rf 1 is a dedendum circle radius starting at the profile base of the secondary rotor, wherein the ratio of the axis distance a of the first axis to the second axis and the addendum circle radius rk 1 a rk 1 is at least 1.636 and at most 1.8, preferably at most 1.733, wherein preferably the main rotor is configured with a wrap-around angle Φ HR, for which it holds that 240° ≤ Φ HR ≤ 360°, and wherein, in a transverse sectional view, a point C is defined on the connecting line ( C 1 C 2) between the first axis and the second axis, at which the pitch circles WK 1 of the secondary rotor and WK 2 of the main rotor touch, that K5 defines the point of intersection of the dedendum circle FK 1 of the secondary rotor with the connecting line ( C 1 C 2), wherein r 1 is the distance between K5 and C, and that K4 designates the point of the suction-side part of the line of engagement which lies farthest spaced apart from the connecting line ( C 1 C 2) between C1 and C2, wherein r 2 is the distance between K4 and C, and wherein it holds that: 0.9 ≤ r 1 r 2 ≤ 0.875 × z 1 z 2 + 0.22 with z 1: number of teeth in the secondary rotor and z 2: number of teeth in the main rotor, and wherein, in a transverse sectional view, circular arcs B 25, B 50, B 75 extending within a secondary rotor tooth are defined, the common center point of which is given by the axis C1, wherein the radius r 25 of B 25 has the value r 25 = rf 1 +0.25*(rk 1 -rf 1), the radius r 50 of B 50 has the value r 50 = rf 1 +0.5*(rk 1 -rf 1), and the radius r 75 of B 75 has the value rf 1 +0.75*(rk 1 -rf 1), and wherein the circular arcs B 25, B 50, B 75 are each delimited by the leading tooth flank F V and trailing tooth flank F N, wherein tooth thickness ratios are defined as ratios of the arc lengths b 25, b 50, b 75 of the circular arcs B 25, B 50, B 75 with ε 1 = b 50 /b 25 and ε 2 = b 75 /b 25, and the following rating is satisfied: 0.65 ≤ ε 1 < 1.0 and/or 0.50 ≤ ε 2 ≤ 0.85, preferably 0.80 ≤ ε 1 < 1.0 and/or 0.50 ≤ ε 2 ≤ 0.79.