How do i get the perfect drill hole width?

[Koolpc]

They don't have to be perfectly round, just roughly to shape and long enuf to sit proud to be cut off flush after hammering home. How do you think fixings were made before wall plugs were invented if wood was not used.

My dad always used to make wooden plugs...

 

[endecotp]

Well i have finally managed it, the grip bar now now securely mounted with four 8x65mm screws

8mm diameter screws?

What size hole, and what size plugs?

 

[Nanako]

8mm diameter screws?

What size hole, and what size plugs?

oops no, thats the dimensions of the plugs, the screws came with them, i linked it earlier in the thread, purchased on recommendation from a post here

 

[slawit]

Once your plug has gone as far as it will go by pushing in with your finger simply insert the screw 3 or 4 threads deep then give it a gently tap the plug will happily drive in flush with the service remove screw job done.

 

[Koolpc]

My Irish uncle used to use a 3 pin plug to fill holes!

 

[blup]

1. How can i make holes that are just right for the plug, that will allow it to go all the way in, but also make it grip properly?

Drill on speed one and deep enough to leave 40mm or so in the brick or block beneath the plaster. Go very slowly through the plaster. Build up the hole size with different size drill bits. Use a quality bit like the Bosch multi construction bit that can be used without hammer action. Fischer nylon plugs grip better than hard plastic rawlplugs

2. How far away from these failed existing holes will i need to drill my next set, in order to make sure that the previous holes don't affect the stability of the new ones? I had the perfect position for this grip bar and i don't want to move it very much from that spot

Using a decent filler you should be able to re use the holes, just drill a bit deeper
Otherwise minimum 50 mm away