Tube insert refers to the outside diameter of the tube.   

Size is the outer diameter 

For example: 25mm round end cap fits a 25mm tube (outside diameter). 

Round end caps  are suitable for protection, covering and finishing pipes.  
To keep water out and stop rusting from inside

Made from plastic  
ribbed for easy fitting,
White colour finish, 

High quality components plastic  which are sturdy and strong for using in different selection of industry.  

Cap size is the same as the outsidediameter (OD) of the tube/ pipe. 

How to measure:

Caps size is determined by the external diameter of the tube. 

For example: external diameter (outside size) of tube 25mm then size of plugs=25mm

The most common pipes have the following section - round​. All plastic plugs are marked exactly like pipes. The outside dimension of the pipe corresponds to the marking of the plug. This is done so that the plugs can be easily selected according to the same size.

Characterized by low abrasiveness ,high dimensional stability even at low temperatures, low water absorption and very good chemical resistance  . It is also characterized by good electroinsulating properties.  It's resistant to changing weather conditions and UV radiation.  

Application: This product is suitable for stainless steel pipe, aluminum pipe, iron pipe, galvanized pipe, square tube, copper pipe, etc. Blockage of various stainless steel products, including furniture, stainless steel doors and other stainless steel decoration  

Features: Good toughness, easy assembly, no deformation, anti slip and wear-resistant, the whole production process is strictly processed 

Note:

1: If the outer diameter is 28mm steel pipe, please select the specification of 28mm 
 2: Pipe plug generally does not say the inner diameter, because the pipe plug has a tooth piece, and it is stuck on the inner wall of the pipe by the tooth piece. The tooth piece will bend due to toughness. Therefore, the pipe wall thickness is between 0.5-2mm, the corresponding plug can be purchased according to the outer diameter of the pipe. If the pipe wall is too thick, the toothpiece can also be cut by itself and then knocked in.