Introduction: Why You Might Need to Swap Your Lock
There are several reasons you might need to replace your door cylinder lock:
- Upgrading security: Moving from a basic lock to TS007 3-Star or SS312 Diamond
- Lost keys: You need new keys but want to keep your existing lock body
- Damaged lock: The cylinder has been snapped, drilled, or worn out
- Moving house: Previous tenant’s keys are still floating around
- Insurance requirement: Your insurer now requires a higher security standard
The good news: Swapping a cylinder lock is a straightforward DIY task. Most homeowners can do it in 15–20 minutes with basic tools. This guide walks you through every step.
Not sure which lock to upgrade to? See our complete door lock comparison guide covering TS007, SS312 Diamond, and security standards.
What You’ll Need: Tools & Materials
Before you start, gather these items:
Tools:
- Screwdriver (usually Phillips head, sometimes flathead)
- Allen keys (if your lock uses hex bolts—check first)
- Measuring tape or ruler
- Small vacuum or compressed air canister (optional, for cleaning)
Materials:
- Your new cylinder lock
- Your old key (to unlock the door during removal)
We stock Rockdoor replacement locks in our shop.
Time required: 15–20 minutes for most people
Difficulty level: Easy (no special skills needed)
Step 1: Understanding Your Lock Protrusion
Why this matters first: Before measuring anything, understand how far your lock currently sticks out from your handle. This affects both security and aesthetics.
External protrusion:
- Look at your external handle and lock from outside
- Does the lock barrel stick out beyond the handle? By how much?
- Ideally, it should sit flush with the handle or slightly recessed
Internal protrusion:
- Check from inside the door
- Does the lock stick out past the internal handle?
- Again, flush-fitting is best
Why flush-fitting matters:
A lock that protrudes creates a grip point for burglars attempting to snap it. A flush lock is harder to grip, harder to snap, and looks more professional. If your current lock sticks out noticeably, consider ordering a smaller cylinder (e.g., 30mm instead of 35mm) to sit flush.
Step 2: Unlock Your Door & Access the Lock
1. Unlock the door fully with your existing key
This step is crucial—it relaxes the internal spring mechanism and makes the cylinder much easier to remove.
2. Locate the retaining screw
Find the small screw on the inside edge of the door, usually near the lock barrel. This holds the cylinder in place.
- On composite doors: The screw is often recessed slightly into the door edge
- On wooden doors: It may be more visible
- If you can’t find it: Check both sides of the door frame (top, middle, or bottom edge)
Pro tip: Take a photo before you start—it helps if you get stuck later.
Step 3: Remove the Retaining Screw & Extract the Old Cylinder
1. Unscrew carefully
Use your screwdriver to remove the retaining screw. Keep it safe—you may need it for the new lock.
2. Insert the key into the lock and turn it slightly (usually to 10 o’clock or 2 o’clock) to align the cam, making it easier to remove the cylinder.
Gently pull the cylinder straight out toward you. It should slide smoothly.
- Don’t force it. If it’s stuck, the door may not be fully unlocked. Unlock again and try once more.
- If still stuck: Apply a tiny drop of graphite lubricant around the cylinder and wait 1–2 minutes, then gently pull.
3. Inspect the old cylinder (optional)
Now that it’s out, you can see the internal mechanism. Notice:
- The length (you’ll need to match this with your new cylinder)
- The condition (is it worn, damaged, or in good shape?)
Step 4: Measure Your Old Cylinder
This is the most critical step. Accurate measurements prevent compatibility issues.
Measure three things:
Overall length (end-to-end):
- Place your ruler along the full length of the cylinder
- Record this measurement (e.g., 80mm)
External length (front face to center hole):
- Measure from the external face (the end that sticks out toward the door’s exterior) to the center hole
- Record this (e.g., 40mm)
Internal length (back face to center hole):
- Measure from the internal face (the back end) to the center hole
- Record this (e.g., 40mm)
Example:
- Overall: 80mm
- External: 40mm / Internal: 40mm (equal split = perfectly balanced)
Not all doors use the same sized cylinder, and some are even offset, i.e 50mm external and 30mm internal.
Why these measurements matter:
- Overall length tells you if the new cylinder will fit your door
- External/Internal split tells you the protrusion ratio and helps you order a flush-fitting replacement
Pro tip: Take a clear photo of your measurements on the old cylinder. Bring this photo when ordering your new lock—retailers can confirm compatibility instantly.
Step 5: Decide on Your New Cylinder Size
Now you can decide whether to:
A) Match the old size (same security, same protrusion)
- Order a cylinder with identical measurements to your old one
B) Downsize for flush-fitting (improved security)
- If your old lock was 50mm external, order 40mm instead
- This makes the lock sit flush with the handle
- Better security: No grip point for burglars to snap
- Better aesthetics: Cleaner, more professional look
Example scenario:
- Old lock: 50mm external (protrudes 10mm beyond handle)
- New order: 40mm external (sits flush with handle)
- Result: More secure, neater appearance
Check compatibility: Ensure your door thickness allows the new size. Most composite doors are 44–48mm thick—confirm this won’t cause issues.
Step 6: Insert the New Cylinder
1. Align the new cylinder
Hold the new cylinder up to the lock barrel and ensure:
- The keyhole faces the correct direction (outward on the external side)
- It’s straight (not tilted or angled)
2. Slide it in smoothly
Insert the new cylinder straight into the barrel. It should go in with gentle pressure—no forcing required.
3. Check alignment
- The cylinder should sit flush with the lock body (no gaps on either side)
- The external/internal split should match your measurements
If it doesn’t feel right, pull it out and check alignment again. Don’t proceed if something feels off.
Step 7: Reinsert the Retaining Screw
1. Align the screw hole
Position the new cylinder so the screw hole aligns perfectly.
2. Reinsert the screw
Screw it back in firmly, but don’t over-tighten. Over-tightening can:
- Damage the lock body
- Crack composite door material
- Make future removal difficult
- Cause the lock to be stiff
3. Test tightness
The cylinder should not rattle when operated with the key. If it does, tighten the screw slightly more.
Step 8: Test Your New Lock
1. Test external side:
- Insert your new key and lift the handle
- Turn smoothly (it shouldn’t be stiff or resistance)
- Withdraw the key
2. Test internal side:
- Use the internal thumbturn (or key, depending on lock type)
- Ensure smooth operation
3. Lock and unlock repeatedly:
- Repeat 5–10 times to ensure consistent, smooth operation
- The action should feel the same every time
4. Try your old key:
- Your old key should NOT work
- This confirms your lock has been successfully changed
5. Final check:
- Ensure the lock bolt extends and retracts fully
- Verify the door closes and locks securely
- Check for any gaps or misalignment around the cylinder
If everything works smoothly, you’re done! ✅
Troubleshooting: Common Issues & Fixes
| Problem | Cause | Solution |
|---|---|---|
| Cylinder won’t slide in | Wrong size or misalignment | Check nothing is blocking the cylinder, ensure the cam is located within the cylinder |
| Key turns but lock doesn’t operate | Cylinder inserted backward | Remove, rotate 180°, and reinsert |
| Cylinder rattles after installation | Retaining screw too loose | Tighten screw gently until rattle stops |
| Key sticks or catches | New cylinder needs lubrication | Apply graphite powder to key, insert/remove 5 times |
| Lock feels stiff | Cylinder binding against locking mechanism | Ensure cylinder is straight and level |
| Old key still works | Cylinder not changed | Replace the cylinder |
When NOT to DIY: Call a Professional
Skip the DIY approach if:
- ❌ You’re replacing the entire lock body (not just the cylinder)
- ❌ Your door has a non-standard configuration
- ❌ The lock is stuck, damaged, or won’t budge after gentle attempts
- ❌ You’re unsure about your door’s internal mechanism
- ❌ Your door warranty requires professional installation
- ❌ The cylinder is genuinely stuck after lubrication attempts
If you’re looking for other Rockdoor spares — handles, hinges, seals or letterplates — see our Rockdoor replacement parts guide.
Professional help costs: £80–£150 for a callout + cylinder swap
Worth it if: You risk damaging your door or lock by forcing it yourself.
What to Upgrade To: TS007 & SS312 Options
Once you’ve mastered the swap process, consider upgrading to a higher-security lock.
Popular upgrades:
- TS007 3-Star: Excellent security, affordable, most insurers require it
- SS312 Diamond: Maximum security, police-approved, premium price
The cost difference from a basic lock is minimal—just £5–£30 more—for significantly better protection.
To measure the cylinder length
Example Measurement
If your measurements are 45mm (internal) and 55mm (external), your cylinder length is 100mm. Ensure you get a replacement cylinder with these same dimensions. If your lock protrudes on the internal or external side, you could reduce these accordingly. Ideally you want them flush or 5mm proud of the handle.
In the example photo above, the overall length of the lock (red line) is 80mm, and you measure from each end of the lock to the center of the hole (yellow lines). In this case, the cylinder lock is a 80mm equal split as it is 40mm / 40mm.
The ‘EXT’ written on the lock tells you that this is the external side that faces to the outside of the door.
Choosing the Best Lock for Your Door
Once you have measured your door cylinder lock, the next step is to choose the best lock for your needs. For a detailed comparison of top-rated locks, read our blog post on Avocet ABS, Ultion Plus, and Yale Platinum locks. This post covers certifications, designs, features, and size ranges to help you make an informed decision on enhancing your home security.
If you have a Rockdoor, the cylinder sits within a precision-engineered locking system — see our guide to Rockdoor features and technical specifications for how the cylinder, Winkhaus lock and aluminium frame all work together.
Frequently Asked Questions
Yes. Swapping a cylinder lock is a simple DIY task that takes 15–20 minutes with just a screwdriver, ruler, and your old key.
15–20 minutes for most people. First-timers may take 25–30 minutes, but it’s straightforward.
A screwdriver, measuring tape or ruler, and optionally an Allen key and graphite lubricant. No specialist tools required.
Measure your old cylinder’s overall length, external length (front to center), and internal length (back to center). Take a photo and show your retailer for confirmation.
Yes. A flush-fitting lock (sitting level with the handle) is harder to snap because burglars can’t grip it. Just confirm your door thickness allows it.
The retaining screw is too loose. Tighten it gently until the rattle stops. Don’t over-tighten or you’ll damage the door.
Minimum: TS007 3-Star (most insurers require it). Maximum: SS312 Diamond. The cost difference is only £5–£30, making upgrades worthwhile.
