Types of pressure nuts:
S - standard nut made of carbon hardened steel. Recommended for use in steel or aluminium sheets with a hardness of 80HRB / 150 HB or less.
CLS - standard stainless steel nut. Recommended for use in steel or aluminum sheets with a hardness of 70 HRB / 125 HB or less.
CLA - standard nut made of aluminum. Recommended for use in aluminum sheets with a hardness of 50HRB / 82HB or less.
SP - is a standard hardened stainless steel nut. Recommended adaptation in stainless steel sheets with a hardness of 90HRB / 185 HB or less.
Note: HRB is Rockwell "B" scale, HB is Hardness Brinel scale.