Between 1/8 and 3/16" I just put a couple of layers of duct tape over the hole. For large cuts on a tire with a fair amount of tread left I super glue a piece of 1/32 ' gasket material meant for pipe flanges over the hole. I cover that with duct tape because the rough edges caused by the glue will fret through the tube. I have used this method on cuts up to 1/2". I only use a tire repaired with the glued on patch on the rear. I have never had one fail.
The gasket material is good for 200 or 300PSI in it's design service..