please tell me where can I get Hex socket Head, M12 x 1.25x20
SW toolbox, 3DCC,McMaster Carr, Traceparts and lot of other website. Else you can take existing available one and modify to required size.
The 1.25 is a not so common pitch, but McMaster-Carr has one listed. Here's the link McMaster-Carr Note that they have 2D and 3D files in several formats for download.
As Deepak points out there are many other sources, but I find McMaster-Carr very easy to use and they have a wide variety of SolidWorks models available.
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