A gearbox actuator, comprising a first external shaft, a second external shaft positioned parallel to the first external shaft, and a locking mechanism configured to prevent accidental horizontal movement of each of the first and second external shafts (102, 104) and/or any relative accidental horizontal movement between the first and second external shafts (102, 104) along their respective lateral axes (LA1, LA2), wherein the locking mechanism comprises a dual-purpose detent pin, comprising two linearly reciprocating detent balls (108a, 108b) capable of linearly reciprocating along a vertical axis, and being provided at opposite ends of the dual-purpose detent pin, a first and second holding structures (110a, 110b) for holding the two linearly reciprocating detent balls (108a, 108b), respectively and are capable of linearly reciprocating along the vertical axis, and wherein the dual-purpose detent pin further comprises a spring being in contact with both the first and second holding structures (110a, 110b), and is configured to allow a pre-determined range of linearly reciprocating opposing motion of at least one of the first and second holding structures (110a, 110b) and at least one of the two linearly reciprocating detent balls (108a, 108b) along the vertical axis, wherein the each of the first and second external shafts (102, 104) comprises at least two crest-like (115, 117) and at least two trough-like (116, 118) sections on its outer surface wherein a first crest-like section of the each of the first and second external shafts (102, 104) is separated from a second crest-like section of the each of the first and second external shafts (102, 104) by a first trough-like section, and characterized in that, a first diameter (α 1 or α 4) of the each of the first and second external shafts (102, 104) at the first crest-like section(s) is different from a second diameter (α 2 or α 5) at the second crest-like section(s) of the each of the first and second external shafts (102, 104). a first external shaft, a second external shaft positioned parallel to the first external shaft, and a locking mechanism configured to prevent accidental horizontal movement of each of the first and second external shafts (102, 104) and/or any relative accidental horizontal movement between the first and second external shafts (102, 104) along their respective lateral axes (LA1, LA2), wherein the locking mechanism comprises a dual-purpose detent pin, comprising two linearly reciprocating detent balls (108a, 108b) capable of linearly reciprocating along a vertical axis, and being provided at opposite ends of the dual-purpose detent pin, a first and second holding structures (110a, 110b) for holding the two linearly reciprocating detent balls (108a, 108b), respectively and are capable of linearly reciprocating along the vertical axis, and wherein the dual-purpose detent pin further comprises a spring being in contact with both the first and second holding structures (110a, 110b), and is configured to allow a pre-determined range of linearly reciprocating opposing motion of at least one of the first and second holding structures (110a, 110b) and at least one of the two linearly reciprocating detent balls (108a, 108b) along the vertical axis, wherein the each of the first and second external shafts (102, 104) comprises at least two crest-like (115, 117) and at least two trough-like (116, 118) sections on its outer surface wherein a first crest-like section of the each of the first and second external shafts (102, 104) is separated from a second crest-like section of the each of the first and second external shafts (102, 104) by a first trough-like section, and two linearly reciprocating detent balls (108a, 108b) capable of linearly reciprocating along a vertical axis, and being provided at opposite ends of the dual-purpose detent pin, a first and second holding structures (110a, 110b) for holding the two linearly reciprocating detent balls (108a, 108b), respectively and are capable of linearly reciprocating along the vertical axis, and wherein the dual-purpose detent pin further comprises a spring being in contact with both the first and second holding structures (110a, 110b), and is configured to allow a pre-determined range of linearly reciprocating opposing motion of at least one of the first and second holding structures (110a, 110b) and at least one of the two linearly reciprocating detent balls (108a, 108b) along the vertical axis, wherein the each of the first and second external shafts (102, 104) comprises at least two crest-like (115, 117) and at least two trough-like (116, 118) sections on its outer surface wherein a first crest-like section of the each of the first and second external shafts (102, 104) is separated from a second crest-like section of the each of the first and second external shafts (102, 104) by a first trough-like section, and characterized in that, a first diameter (α 1 or α 4) of the each of the first and second external shafts (102, 104) at the first crest-like section(s) is different from a second diameter (α 2 or α 5) at the second crest-like section(s) of the each of the first and second external shafts (102, 104).