These relatively thin, large Hookit™ disc holders are typically used with larger 7" or 9" right angle grinders and sanders having a 5/8"-11 shaft.
They are ideal for sanding flat surfaces.
Note that these pads are faced with small Type 1 hooks, and are not suited for use with very coarse discs.
Although marketed as "firm" by 3M, the foam in these pads has a medium density making the pad somewhat conformable to curved surfaces.
The extreme outer edge of the pad is quite flexible.
Priced by the single disc holder.
Heavy on the technical side...
Should you use a soft or firm sanding disc backing pad?
After you have decided between Stikit or Hookit, and chosen no-hole or clean sanding discs, and selected the disc diameter, you will still often be left with the choice of a firm or a soft backing pad.
• As a general rule, you should use coarser abrasive discs on firm backing pads, and finer grit discs on soft backing pads.
Soft Backing Pads
• The advantage of a soft pad is that its surface can flex to some extent, conforming to the shape of the surface being sanded.
This facilitates higher surface contact, more consistent material removal, and less gouging.
• Soft pads are not intended for use with very coarse abrasive discs for heavy duty work, as the higher stresses induced by very coarse abrasives fatigues the foam prematurely.
• Having said that, a soft pad can be used with coarse grit discs for heavy material removal on rounded surfaces - like a sailboat hull - where it would be difficult to maintain full surface contact with a stiffer, firm backing pad.
Just don't expect the soft pad to last as long.
Firm Backing Pads
• Using coarse discs on a firm backing pad works very well, as long as the work surface is flat.
Using a firm pad on a curved surface can easily result in hard-to-remove gouges and scratch marks.
If the surface isn't flat - again, like a sailboat hull - you will generally want to use a softer pad for full surface contact, no matter what the grit of the sanding disc.
• Firm pads are also recommended for leveling uneven surfaces - such as paint brush strokes and runs.
In this application, a soft pad might simply conform to raised areas, rather than cutting them down.