Knowing the names of the parts makes a repair quote readable, whether the quote comes from us or from another Clark County door company. This glossary follows the load: the springs carry the door’s weight, the cables and bottom brackets pass it to the door, the tracks guide it, the seals close it, and the opener only moves it. Where an industry term exists, the names follow DASMA’s glossaries.
Every part below turns up somewhere on our services pages, so a quote that mentions a drum, a bearing plate or a J-arm should make sense after one read. If you are not sure which system your door has, start with our torsion versus extension guide.
Springs and the parts that carry the door’s weight
The counterbalance system holds up almost the whole weight of the door, which is why every part in this group is under tension and none of it is a do-it-yourself repair.
| Part | What it does | How it fails |
|---|---|---|
| Torsion spring | Twists on the shaft above the door to store the energy that lifts it; its size is three numbers (wire diameter, the coil’s inside diameter, length) plus a left or right wind | Breaks from fatigue or rust with a loud bang, and the coil shows a split a few inches wide |
| Extension spring | Stretches above each horizontal track and pulls the door up through cables and pulleys | Snaps or loses tension; without a safety cable the pieces can fly |
| Safety cable | A cable through the center of each extension spring; DASMA calls it a containment cable | Missing or slack, which leaves a breaking spring free to whip across the garage |
| Winding cone | The fitting on a torsion spring’s outer end, with sockets for winding bars and set screws that lock it to the shaft | A cracked casting, or set screws that loosen and let the spring slip |
| Stationary cone | The fitting on the spring’s inner end, bolted to the center bearing plate | Cracks, or works loose from the plate |
| Torsion shaft | The steel shaft or tube that carries the springs and turns the drums | Bends after a spring break or a hard impact, so the drums wobble |
| Center bearing plate | The bracket on the header that supports the shaft and anchors the stationary cones | A worn bearing that grinds, or a plate pulling from a weak header |
| Spring pad | The wooden pad on the header that the center bearing plate bolts to | Splits or loosens, letting the plate shift under load |
| End bearing plates | Brackets at each end of the shaft that hold it level and in line | Worn bearings and loose lag screws |
| Cable drum | A grooved drum at each end of the shaft that winds the lift cable as the door rises | Cracks, or the cable jumps the grooves when it goes slack |
| Lift cable | Braided steel cable from each drum, or over the pulleys, down to the bottom bracket | Frays at the bottom, rusts, or unwinds from the drum so the door hangs crooked |
| Bottom bracket | The bracket at each lower corner that holds the bottom roller and the cable end | Rusts thin at the cable pin; it must never be unbolted while the springs are wound |
| Pulley | Guides the cables on an extension spring door; one rides on each spring | Seizes or cracks and chews the cable |
| Winding bars | Solid steel rods that fit the winding cone to load or unload a torsion spring | Not a part that wears out, but the only safe tool; screwdrivers slip |
When a lift cable hangs loose, the cable hanging loose page explains what to do before anyone touches the door.
Door sections, hinges and struts
A sectional door is a stack of hinged sections that roll up the track one after another, and the parts in this group hold that stack together and stiff.
| Part | What it does | How it fails |
|---|---|---|
| Section | One horizontal panel of the door, hinged to the next | Dents, cracks or skins separating; an HOA tract may need an exact match |
| Stile and rail | The vertical stiles and horizontal rails that frame a section | Wood bottom rails rot; steel ones crease in an impact |
| Hinge | Joins two sections so they pivot; edge hinges also hold a roller and are graduated and numbered by position | Cracks at the knuckle or tears out of the section on a binding door |
| Strut | A stiffener across a section that limits sag when the door is open | Bends, or is missing on a wide door that bows |
| Top fixture | The bracket at each top corner that positions the top roller | Loosens and lets the top section lean away from the jamb |
| Operator reinforcement bracket | The plate on the top section where the opener arm attaches | Tears or cracks the top section when the opener forces a stuck door |
| Handles and gripping points | The places to lift the door by hand; DASMA calls for them near the bottom | Missing on some doors; the seams between sections are never one of them |
Tracks, rollers and the brackets that hold them
The track is the path the door follows and the rollers ride in it, so when either one is bent or worn the door binds, rubs or leaves the track.
| Part | What it does | How it fails |
|---|---|---|
| Vertical track | The upright track beside each jamb | Bends inward from a car or a jammed roller |
| Horizontal track | The track that carries the open door under the ceiling | Sags or twists under added weight |
| Horizontal radius | The curved piece where the vertical and horizontal tracks meet | Rollers jump out here when a cable lets go |
| Flag bracket | The bracket at the top of the vertical track tying it to the jamb and the horizontal track | Loose lag screws let the track pull away |
| Jamb bracket | L-shaped brackets that fasten the vertical track to the jamb | Pull out of soft or rotted jamb wood |
| Back hang | Angle iron hangers holding the back end of the horizontal track to the ceiling | Loosens, letting the back of the track drop |
| Track roller | A wheel on a stem that guides each section; sealed nylon rollers run quieter than bare steel | Cracked wheels, flat spots or seized bearings |
| Roller stem | The shaft of the roller that slides into the hinge or bracket | Bends when the door is forced |
Seals, jambs and the header around the opening
Seals close the gaps around the door, and the jambs and header framing the opening are what the door and every piece of its hardware hang from.
| Part | What it does | How it fails |
|---|---|---|
| Bottom seal | The flexible seal along the bottom edge, which DASMA’s glossary calls an astragal | Tears, flattens, or freezes to the slab |
| Seal retainer | The channel on the bottom section that holds the bottom seal | Bends or corrodes so the seal pulls out |
| Perimeter seal | Weatherstrip along the jambs and header outside the door, also called stop molding | Curls, cracks in the sun, or gaps in the wind |
| Threshold | A strip on the slab that the bottom seal closes against | Loosens or cracks; most useful where the slab drains inward |
| Jamb | The upright framing on each side of the opening | Rots at the slab, splits where track brackets fasten |
| Header | The framing above the opening, which carries the spring pad on a torsion door | A weak header lets the center bearing plate pull loose |
| Headroom, sideroom and backroom | The clear space above, beside and behind the opening that the hardware needs | Too little headroom limits which spring system and opener fit |
Garage door opener parts and safety parts
The opener moves a balanced door rather than lifting a heavy one, and every safety part in this group exists because a moving door can hurt someone.
| Part | What it does | How it fails |
|---|---|---|
| Motor unit | The powerhead on the ceiling, holding the motor, the gear set and the logic board | Hums or clicks without moving when a gear strips or a board fails |
| Drive | Chain, belt, screw or wall-mount; a wall-mount (jackshaft) unit turns the torsion shaft directly | Chains stretch, belts fray, screw drives wear their carriage |
| Rail | The track the trolley rides from the motor to the door | Bends, or works loose at the header bracket |
| Trolley | The carriage on the rail that the door arm hangs from | Its latch wears so the door will not reconnect |
| Door arm (J-arm) | The bent arm from the trolley to the bracket on the top section | Bends when the opener fights a stuck door |
| Emergency release | The red handle on a cord that frees the trolley; federal rules require it red and able to release with 50 pounds of pull or less | Hung out of reach, or pulled on an open door with a bad spring |
| Drive gear and sprocket | The gear set inside the motor unit that turns the chain, belt or screw | Strips, so the motor runs and the door stays put |
| Logic board | The control board that runs the opener’s sequence and reads its safety inputs | Fails and leaves the opener dead or erratic |
| Travel limits and force | The settings for where the door stops and how hard the opener pushes | Drift out of adjustment so the door stops short or reverses |
| Photo eyes | Two sensors near the floor whose beam must be clear for the door to close; entrapment protection is required on openers made from 1993 on | Misaligned, dirty or with a broken wire, often with a blinking opener light |
| Wall control | The button inside the garage, mounted at least five feet up and in sight of the door | Its wire breaks or the button wears out |
For the parts in the first group, garage door spring replacement and cable work are where we start; text a photo of the part and we can name it for you.