Pascal suggested use spirals not actual screw threads lessen file size as I have many bolts.
All was good until I altered a linetype from dashed to continual in layout detail view and suddenly the spirals appeared as above. Unable to solve.
They are doing this only in layout view and only when detail is deactive.
Unfortunately they print as showing to pdf.
I have altered the details back to dashed and 0.9 linewidth but no change.
The items afflicted are Block Instances ,
I have had to turn their layers off to solve it.
Is this a known thing, same very complex 70Mb file as gave dashed circles for normal ones, due to one raster image (see other post, solved by drawing a helix), deformed objects after running a view change only macro, dark fillets (turned out to be a V5 bug)