This super short cage is stainless steel with an integrated brass lock.  It is very short and discreet under clothing.  The cage can be purchased alone, with a firm stainless steel catheter tube, or with a flexible and catheter tube. 

• cage is 33mm diameter x 9mm length 
• the gap for your testicles is 7mm
• cock ring sizes available are 40mm, 45mm, and 50mm
• the sounding flexible tube option is 52mm x 8mm with a 3mm taper for smooth insertion 
• the firm stainless steel tube option is 35mm x 7.5mm with a 5mm taper for smooth insertion 
• each size and sounding option sold separately
• comes with 2 keys