Locking clip is needed when your vehicle retractor is of Emergency Locking Retractor type (ELR, read more: http://bit.ly/2RuF57A).
There are two situations when a locking clip is not needed:
1. CRS has a built-in locking mechanism, OR
2. Seat belt can be locked (using Automatic Locking Retractor (ALR) or Switchable Locking Retractor (SLR)).
There are two types of locking clip:
1. Plastic type – for ECE approved CRS
2. Metal type – for FMVSS approved CRS
Usage instructions differs between the two of them:
1. Plastic type – is used on shoulder part of seat belt which is nearest to the latch plate.
2. Metal type – is used on both shoulder part and lap part of seat belt, which are nearest to the latch plate.
Both type of locking clip should be installed not more than 1 inch from the latch plate.
⚠️ Locking clip should not be used on lap only (2-points) seat belt! ⚠️
Read your vehicle manual and also CRS manual to find out whether you need to use a locking clip when installing a CRS using seat belt.