When using the hat capacity you can either shorten the antenna: mit a 80cm long whip and the top capacity you will have the same efficiency as with the 1.8m long whip.
Or you use the hat capacity and the long whip and achieve better efficiencey especially on the low bands. The capacity is made of one 30cm stainless steel rod with 3/8" thread and the actual capacity made from eight 30cm long, horizontal stainless steel rods.
Note: When using the hat capacity with the 180cm long whip, the resonance frequency is shifted downwards, so that 10 and 12m are not useable anymore. When using the short (145cm) whip with the hat capacity all bands are available, but with reduced efficiency.