NGP 420NA Automatic Door Bottom (H.D.)- Neoprene - Clear - 42"

The NGP 420NA is a heavy-duty surface-mounted automatic door bottom with a neoprene seal, in a clear anodized aluminum finish, sized 42 inches. An automatic door bottom is a retractable drop seal: it seals the gap under a door only when the door is closed, then lifts out of the way when the door opens. That makes the 420NA the right choice for sealing the door undercut against sound, smoke, drafts, light, and energy loss, without the constant floor drag of a fixed door sweep. Made by National Guard Products, it's built for commercial openings and ships with end caps standard.

How an automatic door bottom works

This is what separates an automatic door bottom from a basic sweep, and it's worth understanding before you buy. The 420NA has a spring-loaded plunger on the hinge end. As the door closes, the plunger contacts the frame stop, which trips the mechanism and drops the neoprene seal down against the floor or threshold, closing the gap. When the door opens, the plunger releases and the seal retracts up into the housing, so nothing drags on the floor. That drop-on-close, lift-on-open action is why an automatic door bottom seals better than a sweep while avoiding the wear, drag, and carpet scuffing a fixed sweep causes.

For the best seal, NGP recommends pairing the 420NA with a threshold, so the seal has a clean, level surface to press against. It mounts on the push side of the door.

Where the 420NA fits

The most common reason to specify a heavy-duty automatic door bottom is sound control. The gap under a door is usually the weakest point in any sound-rated wall, so conference rooms, private offices, healthcare consult rooms, and recording or quiet spaces use a drop seal to close that gap. The other big uses are smoke and draft control on corridor and fire-rated doors (paired with perimeter gasketing to seal the whole door edge), and energy and weather sealing on exterior openings. The neoprene seal handles hard flooring well and stands up to commercial cycling.

NGP 420NA specifications

• Type: Surface-mounted, heavy-duty automatic door bottom (retractable drop seal).

• Length: 42 inches. Can be cut down in the field (units 36 inches and longer trim up to about 4 inches; always confirm final length).

• Seal: Neoprene insert (black).

• Housing: Aluminum, clear anodized finish.

• Drop: Up to 7/8 inch maximum drop.

• Mounting: Surface mount, push side of door. Installs without removing the door from its hinges.

• End caps: Furnished standard.

• Performance: BHMA certified to ANSI/BHMA A156.22, 1,000,000-cycle Grade 1, with heat and cold performance testing. UL fire-rated versions available for fire-door assemblies.

• Best practice: Use with a threshold for maximum sealing.

Why choose the NGP 420NA

National Guard Products has built door-sealing and life-safety hardware in the US since 1935, and the 420NA is its heavy-duty surface automatic door bottom, rated for a million cycles. The heavy-duty build and neoprene seal suit high-traffic commercial doors that need a durable, long-lasting seal, and the surface mount makes it a practical retrofit because it installs without pulling the door. The field-cuttable length means one stocked size covers a range of doors, and the standard end caps mean nothing extra to order.

Two things to confirm before ordering: surface-mount units mount on the push side and the end caps add a small amount to the overall width, so account for that against your door width, and if the opening is fire-rated, verify you're using the UL-listed configuration for that assembly. If you need a mortised or semi-mortised version for a cleaner face, those are separate models.

Order the NGP 420NA from American Locksets

We stock NGP door bottoms and gasketing from authorized distribution, so every part ships with a real manufacturer warranty. Compare seals, sizes, and finishes in the automatic door bottoms category, or browse all thresholds and gasketing.