Extrude your Board sketch 10mm (away from you (-z)).
Start a new sketch on the XY plane (rather than the part face - always use origin planes when possible).
Sketch a rectangle as shown out in space.
Add circles at both ends from midpoint of horizontal lines out to endpoint.
Add vertical construction line.
Change horizontal lines to construction.
(there is an easier way to do this dragging arcs out from lines, but if you haven't been taught....)
Add a coincident constraint between the midpoint of the vertical centerline to the projected orgin center point.
Dimension the sketch as shown.
Trim the insides of the arcs.
Then Extrude-Cut through all.
Start the Rectangular Pattern tool and select the slot.
Select the hoizontal line for direction and set to MidPlane.
Set number of copies to 3.
Set distance to 42mm (be sure to change from Spacing to Distance.
It is almost always better to pattern features rather than to pattern sketches.
Start a new part file to create u-bolts.
Sketch a rectangle as shown below the projected origin.
Add a coincident constraint between the top horizontal line and the projected origin.
Add an arc to the top of the rectangle.
Add vertical line from center of arc to top.
Change the lines as shown to construction linetype.
Start a new sketch on the YZ plane (don't create any workplanes that are not needed).
Project Geometry the endpoint of the vertical centerline from sketch1.
Sketch circle at this point diameter 7mm.
Sweep the circle along the u path.
Add the thread features and then the chamers (always do the thread before chamfer to get the correct length).
Save the file as Long U-bolt.
Save As the file Short U-bolt.
The file Short U-bolt should now be the active file.
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