Exit this room and go back to the stairs. This time you really should inspect a chandelier which can be found on the wall (screen). Click on this object and listen to what Van Helsing has to say. Choose the pliers from your inventory and click on the chandelier once again (screen). Ignore the fact that it's now broken and wait for the game to zoom in on what was behind the chandelier. You'll find a new mechanism here and it's going to be your next big puzzle.
Listen to a new suggestion made by our main character. Your task here will be to measure the depth of each hole. As a result, you will have to open your inventory. Combine a tape measure with a spoon and a spool of thread (screen). Choose this new tool, so it'll become your active object.
As you've probably noticed, your new tool is in the lower left corner of the screen. Click on it and use it on all four holes (screen). Each time you've used your tool, you will have to listen to a short statement made by Van Helsing. Measure all four holes and you're going to be rewarded with a new report - Key to Make. Read the report right away and you'll find out that the holes have to be 10, 8, 12 and 5 centimeters deep.
Now you're going to have to go back to the first area of the cellar. You've been there after you've disabled the lock on the large door leading to the manor. This means you'll have to go through the kitchen. Thankfully, you won't come across the butler. Once you're inside the cellar, click on the vise (screen). This tool was previously inactive, but now you're free to use it. Wait for the game to zoom in on the workbench area and take your time to familiarize yourself with the available tools. They can be found to your right and you're going to need all of them to make a spare key.
I guess I should warn you that you're going to spend quite a lot of time creating a new key and you won't be allowed to make any mistakes. Thankfully, if you follow my exact instructions, you're going to make a spare key without having to worry about anything else. Start off by picking up a piece of wood (1). Drag this object and place it directly under the ruler (red area on the screen).
Now you will have to pick up a saw (last item on the list of tools). Make the cut directly under the 10-centimeter mark, because that's how deep the first hole was. Once this is done, pick up this piece of wood once again and place it in the main area of the workbench (screen). It'll occupy the first slot from the top.