vba macro to get thickness of a part

Can you show us an example picture? How did you get the file, is it an imported file?

Not sure what you want to achieve here, how's about measure command ?

how about using the model items button

before

after

the thickness of a part is a a strange thing to determain

the thickness wil be depending on wich plane the part has been drawn

and also on how  u are planning to use the part and how to make the part as the end product ( sheet , round bar, square bar , forging , casting )

in this case its obvius as i inserterted the isometric view of it

mayby for sheet metal there is an option to display the thickness

or in structure it can be displayed in the cutting list but thats only for the stuff u pre define

open part doc and select any face. Then try this macro:

Option Explicit
Sub main()
    Dim swApp As SldWorks.SldWorks
    Dim swModel As SldWorks.ModelDoc2
    Dim swPart As SldWorks.PartDoc
    Dim swSelMgr As SldWorks.SelectionMgr
    Dim swFace As SldWorks.Face2
    Dim arrBody As Variant
    Dim Body As Variant
    Dim arrFaces As Variant
    Dim face As Variant
    Dim swFace2 As SldWorks.Face2
    Dim swBody As SldWorks.Body2
    Dim vPoint1 As Variant
    Dim vPoint2 As Variant
    Dim nDist As Double
    Dim v As MathVector
    Dim v2 As MathVector
    Dim swMath As SldWorks.MathUtility
    Dim swMeasure As SldWorks.measure
    
    Set swApp = Application.SldWorks
    Set swMath = swApp.GetMathUtility


    Set swModel = swApp.ActiveDoc
    Set swPart = swModel
     
    If swPart Is Nothing Then Exit Sub
    Set swSelMgr = swModel.SelectionManager
    If swSelMgr.GetSelectedObjectCount2(-1) <> 1 Then Exit Sub
    If swSelMgr.GetSelectedObjectType3(1, -1) <> swSelFACES Then Exit Sub
    Set swFace = swSelMgr.GetSelectedObject6(1, -1)
    
    Set v = swMath.CreateVector(swFace.Normal)
    Set swMeasure = swModel.Extension.CreateMeasure

    arrBody = swPart.GetBodies2(swSolidBody, True)
    
    If IsEmpty(arrBody) Then Exit Sub
    
    For Each Body In arrBody
        Set swBody = Body
        arrFaces = swBody.GetFaces
        For Each face In arrFaces
            Set swFace2 = face
            Set v2 = swMath.CreateVector(swFace2.Normal)
            If Abs(v.Dot(v2)) = 1 And swApp.IsSame(swFace2, swFace) = swObjectNotSame Then
                'swFace2.Select4 False, Nothing
                nDist = swModel.ClosestDistance(swFace, swFace2, vPoint1, vPoint2) * 1000
                Debug.Print nDist
            End If
        Next
    Next
End Sub

Interesting question!

I think the closest definition to a thickness in 3D is the normal distance between the two equal, largest, planar faces of a part. Once you identify these two large faces. You can pretty much get other thickness  by comparing one of these faces and the other faces (much like Ivana Kolin did).