By Kent · Lock Depot Staff Writer

Soss small invisible hinges: the thickness of the panel decides it

Most of what we sell from Soss is the 200 series that goes into an interior door, a full 1-3/4 in. slab. The smaller hinges are another job. They go into a cabinet door, a panel, a hidden access hatch, a bookcase that swings. The five part numbers people mix up are the 100C, 101C, 103C, 203C and 204C. They look alike on a screen. They do not suit the same material.

The listing for each of them gives a minimum material thickness, and that is the number to start from. A hinge cut into stock that is too thin will break through the face. This article puts the five in one place so you do not have to open five pages.

The five, as listed

Part	Material thickness	Wood screws	Machine screws	Sold as
100C-US26D	1/2 in. minimum, 5/8 in. maximum	#5 x 3/4 in.	#4-40 x 1/2 in.	Two hinges per package
101C-US26D	1/2 in. minimum, 5/8 in. maximum	#5 x 3/4 in.	#4-40 x 1/2 in.	Two hinges per package
103C-US4	3/4 in. minimum	#5 x 3/4 in.	#4-40 x 1/2 in.	Two hinges per package
203C-US4	3/4 in. minimum	#6 x 1 in.	#6-40 x 1/2 in.	A single hinge
204C-US4	3/4 in. minimum	#7 x 1-1/4 in.	#8-32 x 5/8 in.	Two hinges per package

Everything in the table is a cabinet style invisible hinge for wood or metal, a single action hinge that opens a full 180 degrees, non fire rated, and described as a light duty application. The finishes in the table are the ones we picked for the example. Most of these numbers come in several.

Thin stock: the 100C and 101C

These two are the ones for thin material. The listings give a window, 1/2 in. to 5/8 in., and nothing above or below. That is the range of a cabinet door in plywood or a thin hardwood panel. If your panel is 3/4 in., these are not your hinge, and if it is 3/8 in., they are not either.

The product pages list identical thickness and screw data for the 100C and the 101C. We do not have a spec sheet that explains the difference between them, so we will not invent one. If you are replacing one, read the number off the old hinge. If you are choosing new, call us and tell us the panel.

3/4 in. stock: the 103C, 203C and 204C

This is the group for a 3/4 in. panel, the thickness of most cabinet doors and shop-built furniture. The three differ in screw size, and screw size is a proxy for size and load. The 103C takes #5 wood screws, the 203C takes #6, and the 204C takes the biggest, #7 x 1-1/4 in. A bigger screw means a bigger hinge, which is how you step up for a taller or heavier leaf.

The listings do not give a load rating for the group, only "light duty", so we are not going to put a weight on a door and call it fine. If you are hanging something heavy on a 3/4 in. panel, say a full-height cabinet door in solid hardwood, use the 204C and use more than two. Call us with the dimensions and the weight if you are not sure.

203C is sold singly

One trap here. The 203C listing says the page is for a single individual hinge. The 100C, 101C, 103C and 204C pages say two hinges per package. If you order one 203C for a pair of doors, you have one hinge, not a pair. Count before you add to the cart.

Installing: the deep mortise is the work

An invisible hinge sits in a mortise cut into the edge of the door and the edge of the frame. The listing describes it as anchored in a deep, full mortise, which is how it takes load. The pocket has to be cut accurately. A router and a template is how you do it. A router guide template is sold for several sizes in the family, and the 203-IT template is the one listed for the 203 size. The templates for other sizes are separate parts.

All the listed hinges include the screws they need. The riveted hinge pin is non-removable, so when the door is closed nobody can reach the hinge or pull a pin, and the hinge is not visible from the front. That is the security argument for them, and it is a fair one for a small cabinet or a medicine room.

Where these do not belong

None of these is for a fire door, and none is for a heavy slab door. For the larger sizes, see our write-ups of the 208, 212 and 216 hinges and the 218 and 220. If a door needs power through the hinge, read the 218PT power transfer article.

Common questions

Which Soss hinge for 3/4 in. material?

The 103C, 203C and 204C are all listed for a 3/4 in. minimum. The 204C takes the largest screws of the three.

Which for thin material?

The 100C and 101C, listed for material from 1/2 in. to 5/8 in.

Do they open all the way?

Yes. The listings say they open a full 180 degrees and are single action.

Are they fire rated?

No. Every listing here says non fire rated.

Do the screws come with them?

Yes. The listings say the proper size screws are included.

The full line is on our Soss page. Tell us the panel thickness and the weight, and we will match the hinge.