Prime-Line Shower Door Bottom Sweep: Fit Guide

Water leaking under a shower door almost always traces back to one worn strip of vinyl, and a prime-line shower door bottom sweep is the part that fixes it for under $15. Prime-Line dominates the replacement-hardware aisle for a reason: it reverse-engineered sweeps, drip rails, and seals for practically every framed and frameless door built since the 1970s. The catch is that a prime-line shower door bottom sweep only works if you match the profile exactly, and there are more than a dozen profiles that look nearly identical hanging on the peg. This guide is about getting the right part number the first time.

Why Prime-Line Owns This Category

Original shower door manufacturers rarely stock 20-year-old seals. Prime-Line — a hardware maker out of Redlands, California — built its business filling that gap, producing replacement rollers, sweeps, drip rails, and catches for defunct and current brands alike. Its parts carry M-series numbers (M 6259, M 6212, and so on), sold through Home Depot, Ace, Lowe’s, and Amazon, usually for $8 to $20 per piece. When a glass shop quotes you a service call to reseal a door, the part in the tech’s van is very often a Prime-Line strip.

Know Your Door Type First

Sweep profiles divide by door construction, so identify what you have before touching part numbers.

• Framed doors: glass wrapped in aluminum. The sweep is usually a vinyl insert that snap-fits into a channel in the bottom rail, or a drip rail screwed to the outside face with a flexible vinyl fin.
• Frameless doors: bare 3/8 or 1/2 inch glass. The sweep is a clear polycarbonate channel that pushes onto the bottom edge of the glass, with one or two wiper fins hanging down.
• Bypass sliders: often no sweep at all on the panels, but a drip rail on the inner face and vinyl bumpers where panels overlap.

Framed-door parts and frameless-door parts do not interchange, ever. A push-on frameless sweep sized for 3/8-inch glass will not grip 1/4-inch framed glass, and a snap-in vinyl bead has nothing to snap into on a bare panel.

Measuring: The Five Numbers That Matter

Pull the old sweep off (it slides out of a channel or pulls off the glass edge) and take it to the bench. You need:

1. Glass or channel thickness. For frameless, measure the glass with calipers: 1/4, 5/16, 3/8, or 1/2 inch. For framed, measure the slot width in the rail.
2. Overall length. Sweeps come in 32, 36, and 37-inch stock lengths; buy longer and cut down with shears or a fine hacksaw.
3. Fin drop. The distance from the bottom of the glass or rail to the curb, usually 1/2 to 1 inch. Too short leaks; too long drags and howls.
4. Fin count and angle. One wiper, two wipers, or a wiper plus an angled deflector fin that kicks water back into the shower.
5. Profile shape. Match the cross-section of the old part exactly — T-slot insert, snap-in bead, push-on U-channel, or screw-on drip rail.

If the original sweep is missing entirely, measure the gap between door bottom and curb at both ends (out-of-level doors vary), then choose a sweep whose fin drop covers the larger number by about 1/8 inch.

Common Prime-Line Part Numbers

Numbers vary by retailer packaging, but these families cover the bulk of doors I service:

• M 6259 — clear push-on bottom sweep for 3/8-inch frameless glass, 36-inch length, dual fin. The single most-used frameless sweep.
• M 6226 / M 6227 — push-on sweeps for 1/2-inch heavy glass doors.
• M 6212 — one-piece vinyl sweep insert for framed swing doors, T-style, 36 inches.
• M 6war-style drip rails (M 6203, M 6204) — screw-on aluminum drip rails with vinyl inserts for framed doors, typically 32 or 36 inches with end caps.
• M 6109 — bottom seal for framed sliding doors, snap-in style.

Take the old part and your measurements to the store peg or the online listing and compare the printed cross-section diagrams — Prime-Line prints the profile silhouette on every package, which is the fastest way to confirm a match. When in doubt between two profiles, buy both; the wrong one costs less than a second trip.

Replacement Steps: Frameless Push-On Sweep

1. Open the door and pull the old sweep straight down and off; stubborn ones release with a plastic putty knife and a heat gun on low.
2. Scrape residual silicone or scale off the bottom 1 inch of glass with a razor held flat, then wipe with isopropyl alcohol.
3. Cut the new sweep to the exact glass width minus 1/16 inch using shears, deflector fin oriented toward the shower interior.
4. Lubricate the channel with a drop of dish soap in water and press it onto the glass edge, working from the hinge side.
5. Close the door and check the fin contact along the curb — even, light contact is right. Heavy contact means the drop is too long; trim or re-seat.

Replacement Steps: Framed Drip Rail and Insert

1. Back out the two or three screws holding the old drip rail, or slide the vinyl insert out of its channel with pliers.
2. Clean the bottom rail channel — 20 years of soap scum will fight the new insert.
3. Cut the new rail or insert 1/16 inch shy of the door width, reusing the old end caps if the new pack lacks them.
4. Mount screw-on rails with the vinyl fin angled into the shower, bedding the screws in a dab of clear silicone to seal the holes.
5. Operate the door a dozen times and watch for drag; a properly fitted insert whispers, it does not squeal.

Troubleshooting Fit Problems

Sweep will not stay on the glass: the glass is thinner than the channel spec — recheck with calipers, since plenty of “3/8” doors are actually 5/16. Door drags after replacement: fin drop is too long or the door has sagged on its hinges; adjust hinges before cutting the fin. Still leaking at the corners: add Prime-Line splash-guard corner dams ($6 a pair, part M 6218-style) at the curb ends, which stop the sideways sheet of water a sweep cannot catch. Water wicking under the curb itself is not a sweep problem at all — that is failed caulk or tile, a different repair entirely.

Matching Sweeps When the Brand Is Unknown

Half the doors I service have no legible brand anywhere — the label wore off in 1998. The identification workflow that works: photograph the sweep cross-section straight-on against a ruler, measure glass thickness with calipers, and compare against Prime-Line’s online profile diagrams, which show every M-number as a dimensioned silhouette. The Swisco and STB Trading catalogs carry overlapping profiles too, so if Prime-Line lacks your exact shape, cross-reference the same silhouette there. Between the three catalogs I find a match better than 95 percent of the time.

For the last few percent — usually European enclosures with metric extrusions — a universal adhesive-backed sweep is the fallback. It sticks to the door face rather than gripping the edge, seals adequately, and costs about $15. Not elegant, but it beats replacing a whole door because one vinyl strip went extinct.

Tools worth having on hand

• Digital calipers ($20) — the difference between 5/16 and 3/8 glass is invisible by eye
• Heavy shears or a fine-tooth hacksaw for cutting vinyl and polycarbonate cleanly
• Plastic putty knife and heat gun for releasing old sweeps without scratching glass
• Isopropyl alcohol and a flat razor for cleaning the glass edge before refitting

Lifespan and a Buying Tip

Vinyl sweeps harden and split on a 3-to-7-year cycle depending on water chemistry and cleaning habits; chlorine-heavy cleaners accelerate the cracking. When one goes, replace rather than patch — a $12 part protects the bathroom subfloor, and rot repair starts around $1,500. My habit on service calls is to note the part number with a marker on the inside of the bottom rail after each replacement. The next swap becomes a five-minute job with no measuring at all, and any Prime-Line rack in the country will have the strip waiting.