Bulldog Receiver & Coupler Locks: Pin Sizes and MPN Guide

There are two separate places to secure a trailer connection: the hitch receiver on the tow vehicle and the coupler latch on the trailer. They use different locking-pin sizes. Bulldog's Lifelong-series dogbone locks, stainless sleeve-equipped locks and coupler-latch locks look related, but the numbers identify different jobs. This guide compares six exact part numbers so you can select the right style without confusing a receiver pin with a coupler lock.

Receiver lock, coupler latch lock or both?

Receiver hitch lockUse in place of the ordinary retaining pin for a compatible hitch-mounted ball mount, cargo carrier or other receiver accessory. Parts 580401 and 580402 have a 5/8-inch pin for a compatible 2-inch square receiver, with chrome steel and stainless-steel finishes respectively.
Coupler latch lockFits through a suitable trailer coupler's latch locking hole, not the receiver's hitch-pin hole. 580403 is the chrome steel version and 580408 is stainless. Both are listed with a 1/4-inch latch pin; verify the original latch hole and surrounding clearance.
Sleeved lock or combination kit580405 supplies a stainless receiver lock with a sizing sleeve for 1-1/4-inch and 2-inch receiver configurations. 580406 adds a separate trailer coupler lock to the sleeved receiver-lock arrangement.

Bulldog lock comparison by exact manufacturer number

MPN Lock type Pin size Mounting location Difference
580401 Receiver 5/8 in 2 in square receiver 3 in locking span, chrome finish
580402 Receiver 5/8 in 2 in square receiver 3 in locking span, stainless finish
580405 Receiver 1/2 in; 5/8 in with sleeve 1-1/4 or 2 in square receiver Removable sizing sleeve, dust cap
580403 Coupler 1/4 in Compatible coupler latch hole Lifelong-series latch lock, dust cap
580408 Coupler 1/4 in Compatible coupler latch hole Stainless construction, dust cover
580406 Combo set 1/2 in; 5/8 in with sleeve, plus coupler lock 1-1/4 or 2 in receiver plus compatible coupler latch Separate receiver and coupler locking parts
Do not confuse receiver size with pin size. A 2-inch hitch receiver generally calls for a 5/8-inch pin, while the sleeve-equipped 580405 and 580406 accommodate certain 1-1/4-inch receiver arrangements using the smaller 1/2-inch shaft. The coupler-latch locks use a much smaller 1/4-inch pin. Check the actual holes and the locking span before choosing.

Choosing between chrome and stainless steel

The Lifelong 580401 and 580402 have the same manufacturer-listed 3-inch locking span for compatible 2-inch square receiver connections. The 580401 uses chrome-plated steel and 580402 uses stainless steel. Both have a dogbone-style keyed mechanism and a dust cap. In areas with road salt and frequent moisture, material and finish may help you decide; fit, pin diameter and locking clearance still come first.

Measure before ordering

  1. Identify the attachment. A receiver-hitch lock retains the ball mount or accessory shank. A coupler-latch lock secures the trailer's latch. They cannot serve as substitutes for each other.
  2. Check hole diameter. Measure the receiver and accessory pin holes, or the coupler latch hole, and confirm the manufacturer's designated pin size.
  3. Check the locking span. The lock must reach through the receiver walls and accessory with enough clearance for its locking head. Do not assume a pin for a nominal 2-inch receiver also clears every unusually wide hitch assembly.
  4. Use the proper sleeve configuration. For 580405 or the receiver portion of 580406, follow the manufacturer's instructions for 1/2-inch and 5/8-inch pin use. Do not force a sleeve or substitute unrelated pin hardware.
  5. Check what comes in a set. 580406 is a receiver-and-coupler combination. 580405 is the receiver-lock-only option. Match the actual package instead of relying on a generic hitch-pin label.
  6. Test the connection. A lock helps deter removal; it does not increase a hitch's towing capacity, replace a fully seated coupler latch, or substitute for safety chains and the other required towing equipment.

Shop the corresponding Bulldog locks

Each card opens the exact NewRVParts product. Orders ship from supplier warehouses; warehouse viewing or customer pickup is not available.

Related trailer safety connections

For the separate safety-chain and cable connection, see our CURT safety-chain and cable MPN guide. A security lock is not a replacement for the safety connection required by the trailer and tow-vehicle manufacturers.

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