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Gemini (FGT400) User Manual


Gemini logo


Installation guide and user manual

FGT400 Line Diagram



FGT400 Manual Cover

To download this manual as a PDF document, click below. [English]




  1. Outer Tube
  2. Inner Tube
  3. Locking Portion (x2)
  4. 1mm Spacer Ring (x50)
  5. Locking Portion Hex Screw (x2)
  6. 3mm Hex Key
  7. Key (x4)
  8. 19mm Wheel Wrench Adapter
  9. M12 Standard Receiver Wheel Bolt (x2)
  10. M12 Long Receiver Wheel Bolt (x2)

 FGT400 Components

 FGT400 Receiver Bolt


 FGT400 Extend


 FGT400 Positioning



The FullStop® Gemini Wheel Lock is designed to secure twin axle caravans and trailers by locking onto both axles via replacement wheel bolts. Fixed securely to both axles, the Gemini then prohibits normal wheel rotation and consequent movement of the vehicle.

1.   Before the product can be used, two of your existing wheel bolts must be removed and replaced with Receiver Wheel Bolts (9,10). These replacement bolts have been designed to fit the majority of caravan and trailer wheels, however, please check that your existing wheel bolts are of the same specification. The supplied Receiver Bolts (9,10) have M12 x 1.5mm thread pitch with a 60° conical seating. If in any doubt consult the vehicle manufacturer or wheel supplier BEFORE installation as it is possible to damage the hub of the vehicle if the screw threads do not match.

To fit the two necessary receiver bolts (9,10), two of your existing wheel bolts will first need removing. When choosing which two to remove, opt for the inner most wheel bolt on each wheel (see Fig.D and Fig.E for guidance). Where the Gemini Wheel lock can be fitted to any two wheel bolt locations, this positioning is the optimum for initial installation.

Receiver Wheel Bolts (9,10) can be fitted using the Wheel Wrench Adapter (8) which enables you to use a standard 19mm wheel wrench (see Fig.B). The Receiver Bolts (9,10) should be tightened to the correct torque setting for your wheels.

Note: We advise that you initially fit the Standard Receiver Bolts (9) before deciding whether the longer bolts (10) are required. Section 3 of this manual will advise on which wheel bolt length to use with your wheel set up.


Warning iconDo not over-tighten or use an impact wrench on receiver wheel bolts. Check your Owners Manual for details or consult a qualified technician.


FGT400 Install Receiver Bolts


2.   To prepare the Gemini for fitting, the required length must first be determined and adjusted accordingly. To do this, both Locking Portions (3) will need installing for use as guides. Using Fig.A for reference, install the Locking Portions (3) into apertures in the head of both the Outer (1) and Inner Tubes (2). Each Locking Portion (3) can then be secured in place by tightening the Locking Portion Hex Screw (5) using the supplied 3mm Hex Key (6) (see Fig.A for reference).

Next, hold the device up to the wheels, and line the Locking Portion (3) in the head of the Outer Tube (1) up with the Receiver Bolt (9,10) in one of the wheels. From here, gauge whether the length of the Gemini needs to be longer or shorter to allow the Locking Portion (3) in the head of the Inner Tube (2) to line up correctly with the Receiver Bolt (9,10) in the second wheel (see Fig.F for guidance).

To adjust the length of the Gemini Wheel Lock to suit your vehicle, grip the Outer Tube (1) in one hand, and proceed to rotate the Inner Tube (2) in the desired direction (see Fig.C). Use the arrow graphic on the product for reference. Whilst adjusting the length of the Gemini, periodically offer the assembly up to the Receiver Bolts (9,10) in order to correctly judge the required length. Each 360° rotation of the Inner Tube (2) is approximately equal to 1.5mm of length adjustment within a fitting distance range of minimum 510mm and maximum of 825mm (distance between centre of receiver wheel bolts).

NOTE: When shortening the length of the Gemini, ensure that if resistance is met, you do not continue to attempt shortening. This has likely occurred as the minimum length has been met. If in this state the assembly is too long, consider relocating the position of your Receiver Wheel Bolts (9,10) to allow for a wider installation length.


FGT400 Offer up lock


3.   Before using the device it may be necessary to add Spacer Rings (4) to ensure that, when fitted, the ends of the locking portion tubes are as tight as possible to the face of the wheel when the Locking Portion (3) is locked into a Receiver Bolt (9,10). To check this, first fit both sets of keys (7) into their respective Locking Portions (3) and rotate them through 90° clockwise to release the locking ball bearings.

Offer up the assembly to the Receiver Bolts (9,10), guiding the end of the Locking Portions (3) in as far as they will go. Lock them together by rotating the keys (7) anti-clockwise through 90°, then remove both keys (7). The aim at this stage is for the heads of both the Inner (2) and Outer Tubes (1) to be as tight as possible to the face of the wheels, when the Locking Portions (3) are locked into the Receiver Bolts (9,10). Achieving this will mean that the Gemini will be most effective; protecting and preventing access to the Receiver Bolts (9,10) when locked in place. (Fig.G)

FGT400 Installed lock


If there is a gap, or the assembly can be pulled away from the face of the wheel, making the Receiver Bolts (9,10) visible, then Spacer Rings (4) must be used. Try to gauge the amount of gap and add the necessary amount of 1mm thickness Spacer Rings (4) between each Tube (1,2) and respective Locking Portion (3) as shown in Fig.A. Always add an equal sum of spacer rings (4) to each Tube (1,2) .To fix these in place, use the supplied 3mm Hex Key (6) and tighten the Locking Portion Hex Screws (5) into the most applicable of the two available holes in each Tube (1,2) (see Fig.H). The Hex Screws (5) should be tightened to the bodies of the Locking Portions (3) to correctly secure the spacer rings (4) in place.


FGT400 Loosen hex screw


NOTE: If at this stage you find that the Standard Receiver Bolts (9) do not protrude far enough from the wheel to achieve a flush fit of the Gemini Lock with the wheels, it may be that you require the provided longer Receiver Bolts (10). Revert back to section 1, and install the Long Receiver Bolts (10) following the same procedure.

4.   The Gemini Twin Axle Wheel Lock is now ready for use (Fig.I). Please check Receiver Bolt (9,10) torque setting after the first 100 miles (approx) and at regular intervals thereafter.


FGT400 Installed lock


During general use, the length of the Gemini Wheel Lock may need adjustment to suit various receiver bolt locations. In these cases, adjust in the same manner as during set up (Fig.C). Once installed as per this manual, elements such as the Spacer Rings (4) and Receiver Bolt (9,10) fitting should not require amendment, except for maintenance purposes. 

NOTE: In use, some wheel rotation will occur before the Gemini Wheel Lock fully immobilises both axles, thus preventing movement of the vehicle.

TIP: To reduce the amount of length adjustment required between each use, it is possible to add a second Receiver Bolt (9,10) onto each wheel. When doing this, we advise locating the second Receiver Bolts (9,10) in opposing positions to the original Receiver Bolts (9,10); this will allow for a wider range of fitting positions. As per section 1 of this manual, the lock body should still be fitted to the closest two Receiver Bolts (9,10) to prevent excess unwanted wheel rotation.


Warning iconWe do not recommend replacing any more than two wheel bolts on any given wheel.



Grease the lock face and ball bearings before first use, with a light oil such as 3-IN-ONE or equivalent. Thereafter spray any moving parts of the lock body with a light oil such as 3-IN-ONE or equivalent every eight weeks.

Any light scuffs on the gloss surface of the body can often be buffed out with a cloth.



Please store your keys in a safe place and remember to register your product.

Registration is quick and simple, go to Please register within 14 days of purchase. Please retain your original purchase receipt. 



Weight 6.5kg
Height 550mm
Width 60mm
Depth 100mm
Keys Supplied 4



If used properly, your FullStop® product will be an effective deterrent. However, nothing can stop the efforts of the most determined thief, and to this end no liability is accepted for any loss and/or damage caused by any illegal activity including theft or vandalism. Liability also not accepted for any loss and/or damage arising from misuse, unauthorised repair or alteration and failure to follow the user guide directions. No form of consequential loss what so ever will be accepted. 

Photographs for illustration purposes only. Actual product may differ slightly. Purple Line Limited reserve the right to alter product specification without prior notice.