Since version 4.2.0 Gmsh can no longer mesh this CAD (it could up to 4.1.5)
Up to Gmsh 4.1.5 (tested from the official binaries in Linux64), this file could be meshed:
$ gmsh-415 -2 hook.step
Info : Running 'gmsh-415 -2 hook.step' [Gmsh 4.1.5, 1 node, max. 1 thread]
Info : Started on Thu Aug 22 07:50:08 2019
Info : Reading 'hook.step'...
Info : Done reading 'hook.step'
Info : Meshing 1D...
Info : Meshing curve 1 (BSpline)
Info : Meshing curve 2 (BSpline)
[...]
Info : Meshing surface 15 (Torus, MeshAdapt)
Info : Done meshing 2D (0.213494 s)
Info : 498 vertices 1431 elements
Error : ------------------------------
Error : Mesh generation error summary
Error : 8 warnings
Error : 2 errors
Error : Check the full log for details
Error : ------------------------------
Info : Writing 'hook.msh'...
Info : Done writing 'hook.msh'
Info : Stopped on Thu Aug 22 07:50:40 2019
$
It says there were errors but a 2D mesh is obtained.
Since 4.2.0, it enters into an infinite loop:
$ gmsh-420 -2 hook.step
Info : Running 'gmsh-420 -2 hook.step' [Gmsh 4.2.0, 1 node, max. 1 thread]
Info : Started on Thu Aug 22 07:51:36 2019
Info : Reading 'hook.step'...
Info : - Label 'Shapes/Part2/=>[0:1:1:2]/SOLID' (3D)
Info : - Label 'Shapes/Part2/=>[0:1:1:3]/COMPOUND' (3D)
Info : Done reading 'hook.step'
Info : Meshing 1D...
Info : Meshing curve 1 (BSpline)
[...]
Info : 3.64757 84.7776 outside of parametric domain?
Info : 3.64744 84.7776 outside of parametric domain?
Info : 3.64716 84.7775 outside of parametric domain?
Info : 3.64683 84.7774 outside of parametric domain?
Info : 3.64675 84.7774 outside of parametric domain?
Info : 3.64562 84.7771 outside of parametric domain?
Info : 3.6457 84.7772 outside of parametric domain?
Info : 3.64432 84.7768 outside of parametric domain?
Info : 3.64416 84.7768 outside of parametric domain?
Info : 3.64207 84.7763 outside of parametric domain?
Info : 3.31002 51.1709 outside of parametric domain?
Info : 3.64727 84.7775 outside of parametric domain?
Info : 3.64723 84.7775 outside of parametric domain?
[...]
This is also true for current git:
$ gmsh -2 hook.step
Info : Running 'gmsh -2 hook.step' [Gmsh 4.5.0-git-eeeeb9cc3, 1 node, max. 1 thread]
Info : Started on Thu Aug 22 07:52:07 2019
Info : Reading 'hook.step'...
Info : Done reading 'hook.step'
Info : Meshing 1D...
Info : Meshing curve 1 (BSpline)
Info : Meshing curve 2 (BSpline)
[...]
Info : Splits are now done to allow geodesics close to singular points
Info : Splits are now done to allow geodesics close to singular points
Warning : Meshing surface 9 : 2 elements remain invalid
Info : Serializing surface 9 and refining all its bounding edges
Info : Meshing surface 10 (BSpline surface, MeshAdapt)
Info : Meshing surface 11 (Surface of Revolution, MeshAdapt)
Info : Splits are now done to allow geodesics close to singular points
Info : Splits are now done to allow geodesics close to singular points
Info : Splits are now done to allow geodesics close to singular points
[...]