PEM S-Type & CLS-Type · M3 to M8 · Sheet Metal from 0.5mm · Zinc Plated & Stainless Steel
The self clinching nut — also called a press nut or clinch nut — provides permanent, reusable internal (female) threads in thin sheet metal panels. When pressed into a punched hole, the nut's serrated clinching ring causes the surrounding sheet metal to cold-flow into its annular undercut groove, locking it permanently with high push-out and torque-out resistance. The head sits flush after installation — no protrusion, no loose hardware, no welding required. Excel Trading Corporation stocks two types: the PEM S-type equivalent in hardened carbon steel (zinc plated) and the PEM CLS-type equivalent in 300-series stainless steel, in M3 through M8.
Electronics enclosures — server chassis, networking hardware, control panels
Electrical switchboard fabrication — DIN rail mounting, busbar supports, cover plates
Telecom rack enclosures and outdoor cabinets — flush installation, clean interior
Precision sheet metal panels too thin to tap conventionally — aluminium and mild steel
Automotive brackets and subframe panels where welded nuts are not practical
Industrial machine guards, junction boxes and relay panels
Permanent female thread — flush head after installation, clean reverse side
Serrated clinching ring provides high torque-out resistance — cannot rotate under load
Cold-formed undercut locking delivers high push-out resistance from the panel
No welding, heat or adhesive — installed with bench press, hydraulic or pneumatic press
Reusable thread — survives repeated assembly and disassembly without degradation
Two types: S-type hardened carbon steel (zinc plated) and CLS-type 300-series stainless steel
Zinc
Stainless Steel
All sizes available in S-type (zinc plated carbon steel) and CLS-type (stainless steel). Use the longest shank code your sheet thickness allows for maximum push-out resistance.
The self clinching nut is available in two standard types — S-type and CLS-type — each suited to a different combination of panel material and environment. Choosing the correct type is critical. The nut must always be significantly harder than the host panel for the clinching ring to displace the sheet metal into the undercut groove. Install into the wrong panel material and the nut will have near-zero push-out resistance.
Zinc Plated · Hardened · Standard Grade
Made from hardened carbon steel with zinc plating. The standard choice for the vast majority of applications — electronics, switchboards, telecom enclosures and general precision fabrication. Works in steel and aluminium panels up to HRB 80 / HB 150. Harder than CLS-type, giving maximum displacement force and the highest push-out values for a given sheet thickness.
Best for: Server chassis, switchboards, relay panels, telecom enclosures, automotive brackets — indoor and dry environments.
300-Series SS · Passivated · Corrosion Resistant
Made from 300-series austenitic stainless steel, passivated. Fully corrosion resistant in wet, coastal and chemical environments. Because 300-series stainless is softer than hardened carbon steel, CLS-type works only in softer panels — maximum sheet hardness HRB 70 / HB 125. Standard cold-rolled steel typically falls within this limit.
Best for: Outdoor telecom cabinets, coastal installations, food processing panels, marine enclosures — wherever the fastener itself must resist corrosion long-term.
Neither S nor CLS — SP-type required
Stainless steel panels are typically HRB 90 or harder — exceeding the limit for both S-type and CLS-type. Attempting to install either type into stainless sheet will result in near-zero push-out resistance as the clinching ring cannot displace the hard material into the undercut. A specially hardened SP-type nut (PEM SP equivalent) is required.
Contact us on +91-9448239476 if you need clinching fasteners for stainless steel panel applications.
The self clinching nut works through controlled cold-forming of the host sheet. It has three functional zones: the pilot shank, which fits into the punched hole; the serrated clinching ring, which bites into the sheet surface and prevents rotation; and the annular undercut groove between the pilot and the ring body. When a squeezing force is applied, the clinching ring is driven into the sheet surface while simultaneously forcing the sheet metal at the hole edge to flow radially inward and downward into the undercut. This displaced metal permanently locks the nut against pull-out.
The nut head contacts the sheet and stops the press stroke — the nut is now flush on the head side and permanently locked on the shank side. The critical requirement throughout is differential hardness — the nut must always be significantly harder than the host sheet. If the sheet is too hard, the ring cannot displace enough metal into the undercut and push-out resistance will be near zero.
Self clinching nuts must be installed by a squeezing force — a bench press, C-frame press, hydraulic or pneumatic press with flat anvils. The press must apply force perpendicular to the sheet. Never use a hammer or impact tool; uneven force will crack the panel or cock the nut.
Install into bare, uncoated sheet — always
Never install self clinching nuts into painted or powder-coated panels. Coating fills the mounting hole and blocks the undercut — the sheet metal cannot cold-flow and push-out resistance will be near zero. Install into bare sheet metal first, then carry out any painting, powder coating or plating on the full assembly. Also — never deburr or chamfer the mounting hole. Deburring removes the material that must flow into the undercut.
A self clinching nut provides a permanent internal (female) thread in a thin sheet metal panel. It is pressed into a punched hole by a squeezing force. The sheet metal cold-flows into the nut's annular undercut groove, locking it permanently with high push-out and torque-out resistance. A serrated clinching ring prevents rotation under load. The head sits flush after installation. No welding, heat or adhesive required — and the thread is fully reusable.
S-type nuts are hardened carbon steel with zinc plating — the standard choice for electronics, switchboards and general fabrication. They work in steel and aluminium panels up to HRB 80 / HB 150. CLS-type nuts are 300-series stainless steel — fully corrosion resistant but softer, so they work only in panels up to HRB 70 / HB 125. Choose S-type for indoor dry applications. Choose CLS-type when the fastener must resist corrosion in outdoor, wet or coastal environments.
Minimum sheet thickness depends on the shank code. Shank code -1 works from 0.5mm for M3 to M5. Shank code -2 requires a minimum of 1.0mm for M3 to M6. M8 shank code -2 requires 1.0mm and shank code -3 requires 1.4mm. Always use the longest shank code your sheet allows — it gives significantly higher push-out resistance. The sheet must also be bare, uncoated metal within the hardness limit for your chosen nut type.
Paint and powder coating fill the mounting hole and occupy the space where sheet metal must cold-flow into the nut's undercut. If coating is present, the metal cannot displace properly — push-out and torque-out resistance will be severely reduced or near zero. Always install self clinching nuts into bare, uncoated sheet. If the panel will be finished after fabrication, install the nuts first, then coat the complete assembly.
Not with S-type or CLS-type nuts. Stainless steel panels are typically HRB 90 or harder — which exceeds the maximum sheet hardness for both types. If installed, the clinching ring will not displace the panel material adequately and push-out resistance will be near zero. For stainless steel panels, a specially hardened SP-type nut (PEM SP equivalent) is required. Contact us to discuss the correct specification for stainless sheet applications.
Excel Trading Corporation stocks PEM S-type and CLS-type equivalent clinch nuts in M3, M4, M5, M6 and M8 at our Kumbarpet store in Bengaluru. We supply across Karnataka, Tamil Nadu, Andhra Pradesh, Telangana, Kerala and India-wide. Call +91-9448239476 or email info@exceltrading.in for pricing and availability.
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