A ladder comprising: a first assembly having a pair of inner rails and a pair of outer rails, the pair of inner rails being slidably coupled with the pair of outer rails; and at least one locking mechanism comprising: a bracket coupled with a first outer rail of the pair of outer rails, a lever pivotally coupled with the bracket, an engagement pin coupled with the lever and having an engagement portion sized and configured to engage an opening formed in the first outer rail and an aligned opening formed in a first inner rail of the pair of inner rails, the engagement pin including an upper shoulder positioned adjacent the engagement portion, a biasing member biasing the lever towards a first position, and a detent mechanism comprising: a slider body slidably disposed in a detent pocket formed within an interior portion of the lever, a detent spring disposed within the detent pocket and biasing the slider body in a first direction, and a detent groove formed in a portion of the bracket, wherein when the lever is pivoted to a second position relative to the bracket, a portion of the slider body is biased into engagement with the detent groove by the detent spring such that the lever is maintained in the second position until a predetermined force is applied to a specified portion of the lever; characterised in that the upper shoulder of the engagement pin comprises: an interference lip configured to extend upwards along an inner side of the first outer rail when the lever is in the first position; and a recessed portion being spaced from, but being positioned near to the interference lip, wherein the lever is configured to abut and engage the recessed portion when the lever is in the first position. a first assembly having a pair of inner rails and a pair of outer rails, the pair of inner rails being slidably coupled with the pair of outer rails; and at least one locking mechanism comprising: a bracket coupled with a first outer rail of the pair of outer rails, a lever pivotally coupled with the bracket, an engagement pin coupled with the lever and having an engagement portion sized and configured to engage an opening formed in the first outer rail and an aligned opening formed in a first inner rail of the pair of inner rails, the engagement pin including an upper shoulder positioned adjacent the engagement portion, a bracket coupled with a first outer rail of the pair of outer rails, a lever pivotally coupled with the bracket, an engagement pin coupled with the lever and having an engagement portion sized and configured to engage an opening formed in the first outer rail and an aligned opening formed in a first inner rail of the pair of inner rails, the engagement pin including an upper shoulder positioned adjacent the engagement portion, a biasing member biasing the lever towards a first position, and a detent mechanism comprising: a slider body slidably disposed in a detent pocket formed within an interior portion of the lever, a detent spring disposed within the detent pocket and biasing the slider body in a first direction, and a detent groove formed in a portion of the bracket, wherein when the lever is pivoted to a second position relative to the bracket, a portion of the slider body is biased into engagement with the detent groove by the detent spring such that the lever is maintained in the second position until a predetermined force is applied to a specified portion of the lever; characterised in that the upper shoulder of the engagement pin comprises: an interference lip configured to extend upwards along an inner side of the first outer rail when the lever is in the first position; and a recessed portion being spaced from, but being positioned near to the interference lip, wherein the lever is configured to abut and engage the recessed portion when the lever is in the first position. a slider body slidably disposed in a detent pocket formed within an interior portion of the lever, a detent spring disposed within the detent pocket and biasing the slider body in a first direction, and a detent groove formed in a portion of the bracket, wherein when the lever is pivoted to a second position relative to the bracket, a portion of the slider body is biased into engagement with the detent groove by the detent spring such that the lever is maintained in the second position until a predetermined force is applied to a specified portion of the lever; characterised in that the upper shoulder of the engagement pin comprises: an interference lip configured to extend upwards along an inner side of the first outer rail when the lever is in the first position; and a recessed portion being spaced from, but being positioned near to the interference lip, wherein the lever is configured to abut and engage the recessed portion when the lever is in the first position. an interference lip configured to extend upwards along an inner side of the first outer rail when the lever is in the first position; and a recessed portion being spaced from, but being positioned near to the interference lip, wherein the lever is configured to abut and engage the recessed portion when the lever is in the first position.